History log of /openbmc/qemu/hw/hyperv/trace-events (Results 1 – 12 of 12)
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# 99a4706a 22-Oct-2023 Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

Add Hyper-V Dynamic Memory Protocol driver (hv-balloon) hot-add support

One of advantages of using this protocol over ACPI-based PC DIMM hotplug is
that it allows hot-adding memory in much smaller g

Add Hyper-V Dynamic Memory Protocol driver (hv-balloon) hot-add support

One of advantages of using this protocol over ACPI-based PC DIMM hotplug is
that it allows hot-adding memory in much smaller granularity because the
ACPI DIMM slot limit does not apply.

In order to enable this functionality a new memory backend needs to be
created and provided to the driver via the "memdev" parameter.

This can be achieved by, for example, adding
"-object memory-backend-ram,id=mem1,size=32G" to the QEMU command line and
then instantiating the driver with "memdev=mem1" parameter.

The device will try to use multiple memslots to cover the memory backend in
order to reduce the size of metadata for the not-yet-hot-added part of the
memory backend.

Co-developed-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

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# 0d9e8c0b 12-Jun-2023 Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

Add Hyper-V Dynamic Memory Protocol driver (hv-balloon) base

This driver is like virtio-balloon on steroids: it allows both changing the
guest memory allocation via ballooning and (in the next patch

Add Hyper-V Dynamic Memory Protocol driver (hv-balloon) base

This driver is like virtio-balloon on steroids: it allows both changing the
guest memory allocation via ballooning and (in the next patch) inserting
pieces of extra RAM into it on demand from a provided memory backend.

The actual resizing is done via ballooning interface (for example, via
the "balloon" HMP command).
This includes resizing the guest past its boot size - that is, hot-adding
additional memory in granularity limited only by the guest alignment
requirements, as provided by the next patch.

In contrast with ACPI DIMM hotplug where one can only request to unplug a
whole DIMM stick this driver allows removing memory from guest in single
page (4k) units via ballooning.

After a VM reboot the guest is back to its original (boot) size.

In the future, the guest boot memory size might be changed on reboot
instead, taking into account the effective size that VM had before that
reboot (much like Hyper-V does).

For performance reasons, the guest-released memory is tracked in a few
range trees, as a series of (start, count) ranges.
Each time a new page range is inserted into such tree its neighbors are
checked as candidates for possible merging with it.

Besides performance reasons, the Dynamic Memory protocol itself uses page
ranges as the data structure in its messages, so relevant pages need to be
merged into such ranges anyway.

One has to be careful when tracking the guest-released pages, since the
guest can maliciously report returning pages outside its current address
space, which later clash with the address range of newly added memory.
Similarly, the guest can report freeing the same page twice.

The above design results in much better ballooning performance than when
using virtio-balloon with the same guest: 230 GB / minute with this driver
versus 70 GB / minute with virtio-balloon.

During a ballooning operation most of time is spent waiting for the guest
to come up with newly freed page ranges, processing the received ranges on
the host side (in QEMU and KVM) is nearly instantaneous.

The unballoon operation is also pretty much instantaneous:
thanks to the merging of the ballooned out page ranges 200 GB of memory can
be returned to the guest in about 1 second.
With virtio-balloon this operation takes about 2.5 minutes.

These tests were done against a Windows Server 2019 guest running on a
Xeon E5-2699, after dirtying the whole memory inside guest before each
balloon operation.

Using a range tree instead of a bitmap to track the removed memory also
means that the solution scales well with the guest size: even a 1 TB range
takes just a few bytes of such metadata.

Since the required GTree operations aren't present in every Glib version
a check for them was added to the meson build script, together with new
"--enable-hv-balloon" and "--disable-hv-balloon" configure arguments.
If these GTree operations are missing in the system's Glib version this
driver will be skipped during QEMU build.

An optional "status-report=on" device parameter requests memory status
events from the guest (typically sent every second), which allow the host
to learn both the guest memory available and the guest memory in use
counts.

Following commits will add support for their external emission as
"HV_BALLOON_STATUS_REPORT" QMP events.

The driver is named hv-balloon since the Linux kernel client driver for
the Dynamic Memory Protocol is named as such and to follow the naming
pattern established by the virtio-balloon driver.
The whole protocol runs over Hyper-V VMBus.

The driver was tested against Windows Server 2012 R2, Windows Server 2016
and Windows Server 2019 guests and obeys the guest alignment requirements
reported to the host via DM_CAPABILITIES_REPORT message.

Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

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Revision tags: v8.0.0, v7.2.0, v7.0.0, v6.2.0, v6.1.0, v5.2.0
# f00f57f3 13-Sep-2020 Peter Maydell <peter.maydell@linaro.org>

Merge remote-tracking branch 'remotes/alistair/tags/pull-riscv-to-apply-20200910' into staging

This PR includes multiple fixes and features for RISC-V:
- Fixes a bug in printing trap ca

Merge remote-tracking branch 'remotes/alistair/tags/pull-riscv-to-apply-20200910' into staging

This PR includes multiple fixes and features for RISC-V:
- Fixes a bug in printing trap causes
- Allows 16-bit writes to the SiFive test device. This fixes the
failure to reboot the RISC-V virt machine
- Support for the Microchip PolarFire SoC and Icicle Kit
- A reafactor of RISC-V code out of hw/riscv

# gpg: Signature made Thu 10 Sep 2020 19:08:06 BST
# gpg: using RSA key F6C4AC46D4934868D3B8CE8F21E10D29DF977054
# gpg: Good signature from "Alistair Francis <alistair@alistair23.me>" [full]
# Primary key fingerprint: F6C4 AC46 D493 4868 D3B8 CE8F 21E1 0D29 DF97 7054

* remotes/alistair/tags/pull-riscv-to-apply-20200910: (30 commits)
hw/riscv: Sort the Kconfig options in alphabetical order
hw/riscv: Drop CONFIG_SIFIVE
hw/riscv: Always build riscv_hart.c
hw/riscv: Move sifive_test model to hw/misc
hw/riscv: Move sifive_uart model to hw/char
hw/riscv: Move riscv_htif model to hw/char
hw/riscv: Move sifive_plic model to hw/intc
hw/riscv: Move sifive_clint model to hw/intc
hw/riscv: Move sifive_gpio model to hw/gpio
hw/riscv: Move sifive_u_otp model to hw/misc
hw/riscv: Move sifive_u_prci model to hw/misc
hw/riscv: Move sifive_e_prci model to hw/misc
hw/riscv: sifive_u: Connect a DMA controller
hw/riscv: clint: Avoid using hard-coded timebase frequency
hw/riscv: microchip_pfsoc: Hook GPIO controllers
hw/riscv: microchip_pfsoc: Connect 2 Cadence GEMs
hw/arm: xlnx: Set all boards' GEM 'phy-addr' property value to 23
hw/net: cadence_gem: Add a new 'phy-addr' property
hw/riscv: microchip_pfsoc: Connect a DMA controller
hw/dma: Add SiFive platform DMA controller emulation
...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

# Conflicts:
# hw/riscv/trace-events

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# 3d9f371b 12-Sep-2020 Peter Maydell <peter.maydell@linaro.org>

Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-fixes-100920-1' into staging

Various misc and testing fixes:

- Expand CODING_STYLE.rst a little more
- usb-ho

Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-fixes-100920-1' into staging

Various misc and testing fixes:

- Expand CODING_STYLE.rst a little more
- usb-host build fix
- allow check-softfloat unit tests without TCG
- simplify mips imm_branch so compiler isn't confused
- mark ppc64abi32 for deprecation
- more compiler soothing in pch_rev_id
- allow acceptance to skip missing binaries
- more a bunch of plugins to contrib

# gpg: Signature made Thu 10 Sep 2020 10:51:05 BST
# gpg: using RSA key 6685AE99E75167BCAFC8DF35FBD0DB095A9E2A44
# gpg: Good signature from "Alex Bennée (Master Work Key) <alex.bennee@linaro.org>" [full]
# Primary key fingerprint: 6685 AE99 E751 67BC AFC8 DF35 FBD0 DB09 5A9E 2A44

* remotes/stsquad/tags/pull-testing-fixes-100920-1:
plugins: move the more involved plugins to contrib
tests/acceptance: Add Test.fetch_asset(cancel_on_missing=True)
tests: bump avocado version
hw/i386: make explicit clearing of pch_rev_id
configure: don't enable ppc64abi32-linux-user by default
docs/system/deprecated: mark ppc64abi32-linux-user for deprecation
target/mips: simplify gen_compute_imm_branch logic
tests/meson.build: fp tests don't need CONFIG_TCG
usb-host: restrict workaround to new libusb versions
CODING_STYLE.rst: flesh out our naming conventions.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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# c47edb8d 12-Sep-2020 Peter Maydell <peter.maydell@linaro.org>

Merge remote-tracking branch 'remotes/berrange-gitlab/tags/crypt-perf-pull-request' into staging

Improve performance of crypto cipher subsystem

# gpg: Signature made Thu 10 Sep 2020

Merge remote-tracking branch 'remotes/berrange-gitlab/tags/crypt-perf-pull-request' into staging

Improve performance of crypto cipher subsystem

# gpg: Signature made Thu 10 Sep 2020 11:05:18 BST
# gpg: using RSA key DAF3A6FDB26B62912D0E8E3FBE86EBB415104FDF
# gpg: Good signature from "Daniel P. Berrange <dan@berrange.com>" [full]
# gpg: aka "Daniel P. Berrange <berrange@redhat.com>" [full]
# Primary key fingerprint: DAF3 A6FD B26B 6291 2D0E 8E3F BE86 EBB4 1510 4FDF

* remotes/berrange-gitlab/tags/crypt-perf-pull-request:
crypto/gcrypt: Split QCryptoCipherGcrypt into subclasses
crypto/nettle: Split QCryptoCipherNettle into subclasses
crypto/builtin: Split QCryptoCipherBuiltin into subclasses
crypto/builtin: Split and simplify AES_encrypt_cbc
crypto/builtin: Move AES_cbc_encrypt into cipher-builtin.inc.c
crypto/builtin: Merge qcrypto_cipher_aes_{ecb,xts}_{en,de}crypt
crypto/builtin: Remove odd-sized AES block handling
crypto: Constify cipher data tables
crypto: Move cipher->driver init to qcrypto_*_cipher_ctx_new
crypto: Allocate QCryptoCipher with the subclass
crypto: Use the correct const type for driver
crypto: Move QCryptoCipherDriver typedef to crypto/cipher.h
crypto/nettle: Fix xts_encrypt arguments
crypto: Remove redundant includes
crypto: Rename cipher include files to .c.inc
crypto: Assume blocksize is a power of 2
tests: fix output message formatting for crypto benchmarks

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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# 842038f5 12-Sep-2020 Peter Maydell <peter.maydell@linaro.org>

Merge remote-tracking branch 'remotes/vivier2/tags/trivial-branch-for-5.2-pull-request' into staging

trivial patches pull request 20200911

# gpg: Signature made Fri 11 Sep 2020 20:3

Merge remote-tracking branch 'remotes/vivier2/tags/trivial-branch-for-5.2-pull-request' into staging

trivial patches pull request 20200911

# gpg: Signature made Fri 11 Sep 2020 20:32:27 BST
# gpg: using RSA key CD2F75DDC8E3A4DC2E4F5173F30C38BD3F2FBE3C
# gpg: issuer "laurent@vivier.eu"
# gpg: Good signature from "Laurent Vivier <lvivier@redhat.com>" [full]
# gpg: aka "Laurent Vivier <laurent@vivier.eu>" [full]
# gpg: aka "Laurent Vivier (Red Hat) <lvivier@redhat.com>" [full]
# Primary key fingerprint: CD2F 75DD C8E3 A4DC 2E4F 5173 F30C 38BD 3F2F BE3C

* remotes/vivier2/tags/trivial-branch-for-5.2-pull-request:
target/i386/kvm: Add missing fallthrough comment
util/hexdump: Reorder qemu_hexdump() arguments
util/hexdump: Convert to take a void pointer argument
hw/arm/pxa2xx: Add missing fallthrough comment
target/i386/kvm: Rename host_tsx_blacklisted() as host_tsx_broken()
test-vmstate: remove unnecessary code in match_interval_mapping_node
hw: hyperv: vmbus: Fix 32bit compilation
kconfig: fix comment referring to old Makefiles
meson.build: tweak sdl-image error message
hw/net/e1000e: Remove duplicated write handler for FLSWDATA register
hw/net/e1000e: Remove overwritten read handler for STATUS register
Makefile: Skip the meson subdir in cscope/TAGS/ctags
Makefile: Drop extra phony cscope
hw/gpio/max7310: Replace disabled printf() by qemu_log_mask(UNIMP)
hw/gpio/omap_gpio: Replace fprintf() by qemu_log_mask(GUEST_ERROR)
hw/acpi/tco: Remove unused definitions
hw/isa/isa-bus: Replace hw_error() by assert()
hw/mips/fuloong2e: Convert pointless error message to an assert()

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

# Conflicts:
# net/colo-compare.c

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# f4ef8c9c 11-Sep-2020 Peter Maydell <peter.maydell@linaro.org>

Merge remote-tracking branch 'remotes/ehabkost/tags/machine-next-pull-request' into staging

QOM boilerplate cleanup

Documentation build fix:
* memory: Remove kernel-doc comment

Merge remote-tracking branch 'remotes/ehabkost/tags/machine-next-pull-request' into staging

QOM boilerplate cleanup

Documentation build fix:
* memory: Remove kernel-doc comment marker (Eduardo Habkost)

QOM cleanups:
* Rename QOM macros for consistency between
TYPE_* and type checking constants (Eduardo Habkost)

QOM new macros:
* OBJECT_DECLARE_* and OBJECT_DEFINE_* macros (Daniel P. Berrangé)
* DECLARE_*_CHECKER macros (Eduardo Habkost)

Automated QOM boilerplate changes:
* Automated changes to use DECLARE_*_CHECKER (Eduardo Habkost
* Automated changes to use OBJECT_DECLARE* (Eduardo Habkost)

# gpg: Signature made Thu 10 Sep 2020 19:17:49 BST
# gpg: using RSA key 5A322FD5ABC4D3DBACCFD1AA2807936F984DC5A6
# gpg: issuer "ehabkost@redhat.com"
# gpg: Good signature from "Eduardo Habkost <ehabkost@redhat.com>" [full]
# Primary key fingerprint: 5A32 2FD5 ABC4 D3DB ACCF D1AA 2807 936F 984D C5A6

* remotes/ehabkost/tags/machine-next-pull-request: (33 commits)
virtio-vga: Use typedef name for instance_size
vhost-user-vga: Use typedef name for instance_size
xilinx_axienet: Use typedef name for instance_size
lpc_ich9: Use typedef name for instance_size
omap_intc: Use typedef name for instance_size
xilinx_axidma: Use typedef name for instance_size
tusb6010: Rename TUSB to TUSB6010
pc87312: Rename TYPE_PC87312_SUPERIO to TYPE_PC87312
vfio: Rename PCI_VFIO to VFIO_PCI
usb: Rename USB_SERIAL_DEV to USB_SERIAL
sabre: Rename SABRE_DEVICE to SABRE
rs6000_mc: Rename RS6000MC_DEVICE to RS6000MC
filter-rewriter: Rename FILTER_COLO_REWRITER to FILTER_REWRITER
esp: Rename ESP_STATE to ESP
ahci: Rename ICH_AHCI to ICH9_AHCI
vmgenid: Rename VMGENID_DEVICE to TYPE_VMGENID
vfio: Rename VFIO_AP_DEVICE_TYPE to TYPE_VFIO_AP_DEVICE
dev-smartcard-reader: Rename CCID_DEV_NAME to TYPE_USB_CCID_DEV
ap-device: Rename AP_DEVICE_TYPE to TYPE_AP_DEVICE
gpex: Fix type checking function name
...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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# 2499453e 11-Sep-2020 Peter Maydell <peter.maydell@linaro.org>

Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches:

- qemu-img create: Fail gracefully when backing file is an empty string
- Fixes

Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches:

- qemu-img create: Fail gracefully when backing file is an empty string
- Fixes related to filter block nodes ("Deal with filters" series)
- block/nvme: Various cleanups required to use multiple queues
- block/nvme: Use NvmeBar structure from "block/nvme.h"
- file-win32: Fix "locking" option
- iotests: Allow running from different directory

# gpg: Signature made Thu 10 Sep 2020 10:11:19 BST
# gpg: using RSA key DC3DEB159A9AF95D3D7456FE7F09B272C88F2FD6
# gpg: issuer "kwolf@redhat.com"
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>" [full]
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74 56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream: (65 commits)
block/qcow2-cluster: Add missing "fallthrough" annotation
block/nvme: Pair doorbell registers
block/nvme: Use generic NvmeBar structure
block/nvme: Group controller registers in NVMeRegs structure
file-win32: Fix "locking" option
iotests: Allow running from different directory
iotests: Test committing to overridden backing
iotests: Add test for commit in sub directory
iotests: Add filter mirror test cases
iotests: Add filter commit test cases
iotests: Let complete_and_wait() work with commit
iotests: Test that qcow2's data-file is flushed
block: Leave BDS.backing_{file,format} constant
block: Inline bdrv_co_block_status_from_*()
blockdev: Fix active commit choice
block: Drop backing_bs()
qemu-img: Use child access functions
nbd: Use CAF when looking for dirty bitmap
commit: Deal with filters
backup: Deal with filters
...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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# b15e402f 06-Aug-2020 Markus Armbruster <armbru@redhat.com>

trace-events: Fix attribution of trace points to source

Some trace points are attributed to the wrong source file. Happens
when we neglect to update trace-events for code motion, or add

trace-events: Fix attribution of trace points to source

Some trace points are attributed to the wrong source file. Happens
when we neglect to update trace-events for code motion, or add events
in the wrong place, or misspell the file name.

Clean up with help of scripts/cleanup-trace-events.pl. Funnies
requiring manual post-processing:

* accel/tcg/cputlb.c trace points are in trace-events.

* block.c and blockdev.c trace points are in block/trace-events.

* hw/block/nvme.c uses the preprocessor to hide its trace point use
from cleanup-trace-events.pl.

* hw/tpm/tpm_spapr.c uses pseudo trace point tpm_spapr_show_buffer to
guard debug code.

* include/hw/xen/xen_common.h trace points are in hw/xen/trace-events.

* linux-user/trace-events abbreviates a tedious list of filenames to
*/signal.c.

* net/colo-compare and net/filter-rewriter.c use pseudo trace points
colo_compare_miscompare and colo_filter_rewriter_debug to guard
debug code.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200806141334.3646302-5-armbru@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

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# 5acc270a 25-Jun-2020 Peter Maydell <peter.maydell@linaro.org>

Merge remote-tracking branch 'remotes/xtensa/tags/20200625-xtensa' into staging

target/xtensa fixes for 5.1:

- fix access to special registers missing in the core configuration;

Merge remote-tracking branch 'remotes/xtensa/tags/20200625-xtensa' into staging

target/xtensa fixes for 5.1:

- fix access to special registers missing in the core configuration;
- fix simcall opcode behavior for new hardware;
- drop gen_io_end call from xtensa translator.

# gpg: Signature made Thu 25 Jun 2020 09:08:58 BST
# gpg: using RSA key 2B67854B98E5327DCDEB17D851F9CC91F83FA044
# gpg: issuer "jcmvbkbc@gmail.com"
# gpg: Good signature from "Max Filippov <filippov@cadence.com>" [unknown]
# gpg: aka "Max Filippov <max.filippov@cogentembedded.com>" [full]
# gpg: aka "Max Filippov <jcmvbkbc@gmail.com>" [full]
# Primary key fingerprint: 2B67 854B 98E5 327D CDEB 17D8 51F9 CC91 F83F A044

* remotes/xtensa/tags/20200625-xtensa:
target/xtensa: drop gen_io_end call
target/xtensa: fix simcall for newer hardware
target/xtensa: fetch HW version from configuration overlay
target/xtensa: work around missing SR definitions

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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# 7d3660e7 12-Jun-2020 Peter Maydell <peter.maydell@linaro.org>

Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

* Miscellaneous fixes and feature enablement (many)
* SEV refactoring (David)
* Hyper-V initial support

Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

* Miscellaneous fixes and feature enablement (many)
* SEV refactoring (David)
* Hyper-V initial support (Jon)
* i386 TCG fixes (x87 and SSE, Joseph)
* vmport cleanup and improvements (Philippe, Liran)
* Use-after-free with vCPU hot-unplug (Nengyuan)
* run-coverity-scan improvements (myself)
* Record/replay fixes (Pavel)
* -machine kernel_irqchip=split improvements for INTx (Peter)
* Code cleanups (Philippe)
* Crash and security fixes (PJP)
* HVF cleanups (Roman)

# gpg: Signature made Fri 12 Jun 2020 16:57:04 BST
# gpg: using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg: issuer "pbonzini@redhat.com"
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [full]
# gpg: aka "Paolo Bonzini <pbonzini@redhat.com>" [full]
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4 E2F7 7E15 100C CD36 69B1
# Subkey fingerprint: F133 3857 4B66 2389 866C 7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream: (116 commits)
target/i386: Remove obsolete TODO file
stubs: move Xen stubs to accel/
replay: fix replay shutdown for console mode
exec/cpu-common: Move MUSB specific typedefs to 'hw/usb/hcd-musb.h'
hw/usb: Move device-specific declarations to new 'hcd-musb.h' header
exec/memory: Remove unused MemoryRegionMmio type
checkpatch: reversed logic with acpi test checks
target/i386: sev: Unify SEVState and SevGuestState
target/i386: sev: Remove redundant handle field
target/i386: sev: Remove redundant policy field
target/i386: sev: Remove redundant cbitpos and reduced_phys_bits fields
target/i386: sev: Partial cleanup to sev_state global
target/i386: sev: Embed SEVState in SevGuestState
target/i386: sev: Rename QSevGuestInfo
target/i386: sev: Move local structure definitions into .c file
target/i386: sev: Remove unused QSevGuestInfoClass
xen: fix build without pci passthrough
i386: hvf: Drop HVFX86EmulatorState
i386: hvf: Move mmio_buf into CPUX86State
i386: hvf: Move lazy_flags into CPUX86State
...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

# Conflicts:
# hw/i386/acpi-build.c

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Revision tags: v5.0.0
# 0d71f708 24-Apr-2020 Jon Doron <arilou@gmail.com>

vmbus: vmbus implementation

Add the VMBus infrastructure -- bus, devices, root bridge, vmbus state
machine, vmbus channel interactions, etc.

VMBus is a collection of technologie

vmbus: vmbus implementation

Add the VMBus infrastructure -- bus, devices, root bridge, vmbus state
machine, vmbus channel interactions, etc.

VMBus is a collection of technologies. At its lowest layer, it's a message
passing and signaling mechanism, allowing efficient passing of messages to and
from guest VMs. A layer higher, it's a mechanism for defining channels of
communication, where each channel is tagged with a type (which implies a
protocol) and a instance ID. A layer higher than that, it's a bus driver,
serving as the basis of device enumeration within a VM, where a channel can
optionally be exposed as a paravirtual device. When a server-side (paravirtual
back-end) component wishes to offer a channel to a guest VM, it does so by
specifying a channel type, a mode, and an instance ID. VMBus then exposes this
in the guest.

More information about VMBus can be found in the file
vmbuskernelmodeclientlibapi.h in Microsoft's WDK.

TODO:
- split into smaller palatable pieces
- more comments
- check and handle corner cases

Kudos to Evgeny Yakovlev (formerly eyakovlev@virtuozzo.com) and Andrey
Smetatin (formerly asmetanin@virtuozzo.com) for research and
prototyping.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: Jon Doron <arilou@gmail.com>
Message-Id: <20200424123444.3481728-4-arilou@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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