Searched hist:edea7c4f (Results 1 – 2 of 2) sorted by relevance
| /openbmc/linux/arch/x86/kvm/mmu/ |
| H A D | spte.c | edea7c4f Thu Feb 25 14:47:45 CST 2021 Sean Christopherson <seanjc@google.com> KVM: x86/mmu: Use a dedicated bit to track shadow/MMU-present SPTEs
Introduce MMU_PRESENT to explicitly track which SPTEs are "present" from
the MMU's perspective. Checking for shadow-present SPTEs is a very
common operation for the MMU, particularly in hot paths such as page
faults. With the addition of "removed" SPTEs for the TDP MMU,
identifying shadow-present SPTEs is quite costly especially since it
requires checking multiple 64-bit values.
On 64-bit KVM, this reduces the footprint of kvm.ko's .text by ~2k bytes.
On 32-bit KVM, this increases the footprint by ~200 bytes, but only
because gcc now inlines several more MMU helpers, e.g. drop_parent_pte().
We now need to drop bit 11, used for the MMU_PRESENT flag, from
the set of bits used to store the generation number in MMIO SPTEs.
Otherwise MMIO SPTEs with bit 11 set would get false positives for
is_shadow_present_spte() and lead to a variety of fireworks, from oopses
to likely hangs of the host kernel.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-21-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|
| H A D | spte.h | edea7c4f Thu Feb 25 14:47:45 CST 2021 Sean Christopherson <seanjc@google.com> KVM: x86/mmu: Use a dedicated bit to track shadow/MMU-present SPTEs
Introduce MMU_PRESENT to explicitly track which SPTEs are "present" from
the MMU's perspective. Checking for shadow-present SPTEs is a very
common operation for the MMU, particularly in hot paths such as page
faults. With the addition of "removed" SPTEs for the TDP MMU,
identifying shadow-present SPTEs is quite costly especially since it
requires checking multiple 64-bit values.
On 64-bit KVM, this reduces the footprint of kvm.ko's .text by ~2k bytes.
On 32-bit KVM, this increases the footprint by ~200 bytes, but only
because gcc now inlines several more MMU helpers, e.g. drop_parent_pte().
We now need to drop bit 11, used for the MMU_PRESENT flag, from
the set of bits used to store the generation number in MMIO SPTEs.
Otherwise MMIO SPTEs with bit 11 set would get false positives for
is_shadow_present_spte() and lead to a variety of fireworks, from oopses
to likely hangs of the host kernel.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-21-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|