Commit 0cbc60d4 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Use 16-bit fields to track dirty/valid emulator GPRs 



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, maxing out at 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).

Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220526210817.3428868-5-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a5ba67b4

arch/x86/kvm/emulate.c

+3 −0
Original line number Diff line number Diff line
@@ -262,6 +262,9 @@ static ulong *reg_write(struct x86_emulate_ctxt *ctxt, unsigned nr) 
	if (WARN_ON_ONCE(nr >= NR_EMULATOR_GPRS))

		nr &= NR_EMULATOR_GPRS - 1;



	BUILD_BUG_ON(sizeof(ctxt->regs_dirty) * BITS_PER_BYTE < NR_EMULATOR_GPRS);

	BUILD_BUG_ON(sizeof(ctxt->regs_valid) * BITS_PER_BYTE < NR_EMULATOR_GPRS);



	ctxt->regs_valid |= 1 << nr;

	ctxt->regs_dirty |= 1 << nr;

	return &ctxt->_regs[nr];

arch/x86/kvm/kvm_emulate.h

+2 −2
Original line number Diff line number Diff line
@@ -356,9 +356,9 @@ struct x86_emulate_ctxt { 
	u8 lock_prefix;

	u8 rep_prefix;

	/* bitmaps of registers in _regs[] that can be read */

	u32 regs_valid;

	u16 regs_valid;

	/* bitmaps of registers in _regs[] that have been written */

	u32 regs_dirty;

	u16 regs_dirty;

	/* modrm */

	u8 modrm;

	u8 modrm_mod;