Messages in this thread | | | Date | Thu, 26 May 2022 08:41:04 -0700 | From | Kees Cook <> | Subject | Re: [PATCH 4/4] KVM: x86: Use 16-bit fields to track dirty/valid emulator GPRs |
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On Wed, May 25, 2022 at 10:26:04PM +0000, Sean Christopherson wrote: > Use a u16 instead of a u32 to track the dirty/valid status of GPRs in the > emulator. Unlike struct kvm_vcpu_arch, x86_emulate_ctxt tracks only the > "true" GPRs, i.e. doesn't include RIP in its array, and so only needs to > track 16 registers. > > Note, having 16 GPRs is a fundamental property of x86-64 and will not > change barring a massive architecture update. Legacy x86 ModRM and SIB > encodings use 3 bits for GPRs, i.e. support 8 registers. x86-64 uses a > single bit in the REX prefix for each possible reference type to double > the number of supported GPRs to 16 registers (4 bits). > > Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
-- Kees Cook
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