From f8052a053a7af2a53288901d27d6419e100ad8e2 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Thu, 9 Jan 2020 15:06:39 -0800 Subject: [PATCH] KVM: x86/mmu: Reorder the reserved bit check in prefetch_invalid_gpte() Move the !PRESENT and !ACCESSED checks in FNAME(prefetch_invalid_gpte) above the call to is_rsvd_bits_set(). For a well behaved guest, the !PRESENT and !ACCESSED are far more likely to evaluate true than the reserved bit checks, and they do not require additional memory accesses. Before: Dump of assembler code for function paging32_prefetch_invalid_gpte: 0x0000000000044240 <+0>: callq 0x44245 0x0000000000044245 <+5>: mov %rcx,%rax 0x0000000000044248 <+8>: shr $0x7,%rax 0x000000000004424c <+12>: and $0x1,%eax 0x000000000004424f <+15>: lea 0x0(,%rax,4),%r8 0x0000000000044257 <+23>: add %r8,%rax 0x000000000004425a <+26>: mov %rcx,%r8 0x000000000004425d <+29>: and 0x120(%rsi,%rax,8),%r8 0x0000000000044265 <+37>: mov 0x170(%rsi),%rax 0x000000000004426c <+44>: shr %cl,%rax 0x000000000004426f <+47>: and $0x1,%eax 0x0000000000044272 <+50>: or %rax,%r8 0x0000000000044275 <+53>: jne 0x4427c 0x0000000000044277 <+55>: test $0x1,%cl 0x000000000004427a <+58>: jne 0x4428a 0x000000000004427c <+60>: mov %rdx,%rsi 0x000000000004427f <+63>: callq 0x44080 0x0000000000044284 <+68>: mov $0x1,%eax 0x0000000000044289 <+73>: retq 0x000000000004428a <+74>: xor %eax,%eax 0x000000000004428c <+76>: and $0x20,%ecx 0x000000000004428f <+79>: jne 0x44289 0x0000000000044291 <+81>: mov %rdx,%rsi 0x0000000000044294 <+84>: callq 0x44080 0x0000000000044299 <+89>: mov $0x1,%eax 0x000000000004429e <+94>: jmp 0x44289 End of assembler dump. After: Dump of assembler code for function paging32_prefetch_invalid_gpte: 0x0000000000044240 <+0>: callq 0x44245 0x0000000000044245 <+5>: test $0x1,%cl 0x0000000000044248 <+8>: je 0x4424f 0x000000000004424a <+10>: test $0x20,%cl 0x000000000004424d <+13>: jne 0x4425d 0x000000000004424f <+15>: mov %rdx,%rsi 0x0000000000044252 <+18>: callq 0x44080 0x0000000000044257 <+23>: mov $0x1,%eax 0x000000000004425c <+28>: retq 0x000000000004425d <+29>: mov %rcx,%rax 0x0000000000044260 <+32>: mov (%rsi),%rsi 0x0000000000044263 <+35>: shr $0x7,%rax 0x0000000000044267 <+39>: and $0x1,%eax 0x000000000004426a <+42>: lea 0x0(,%rax,4),%r8 0x0000000000044272 <+50>: add %r8,%rax 0x0000000000044275 <+53>: mov %rcx,%r8 0x0000000000044278 <+56>: and 0x120(%rsi,%rax,8),%r8 0x0000000000044280 <+64>: mov 0x170(%rsi),%rax 0x0000000000044287 <+71>: shr %cl,%rax 0x000000000004428a <+74>: and $0x1,%eax 0x000000000004428d <+77>: mov %rax,%rcx 0x0000000000044290 <+80>: xor %eax,%eax 0x0000000000044292 <+82>: or %rcx,%r8 0x0000000000044295 <+85>: je 0x4425c 0x0000000000044297 <+87>: mov %rdx,%rsi 0x000000000004429a <+90>: callq 0x44080 0x000000000004429f <+95>: mov $0x1,%eax 0x00000000000442a4 <+100>: jmp 0x4425c End of assembler dump. Signed-off-by: Sean Christopherson Reviewed-by: Vitaly Kuznetsov Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/paging_tmpl.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index b53bed3c901c..1fde6a1c506d 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -175,9 +175,6 @@ static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, u64 *spte, u64 gpte) { - if (is_rsvd_bits_set(vcpu->arch.mmu, gpte, PT_PAGE_TABLE_LEVEL)) - goto no_present; - if (!FNAME(is_present_gpte)(gpte)) goto no_present; @@ -186,6 +183,9 @@ static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu, !(gpte & PT_GUEST_ACCESSED_MASK)) goto no_present; + if (is_rsvd_bits_set(vcpu->arch.mmu, gpte, PT_PAGE_TABLE_LEVEL)) + goto no_present; + return false; no_present: