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KVM: x86: use kvm_read_guest_page for emulator accesses

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Emulator accesses are always done a page at a time, either by the emulator
itself (for fetches) or because we need to query the MMU for address
translations.  Speed up these accesses by using kvm_read_guest_page
and, in the case of fetches, by inlining kvm_read_guest_virt_helper and
dropping the loop around kvm_read_guest_page.

This final tweak saves 30-100 more clock cycles (4-10%), bringing the
count (as measured by kvm-unit-tests) down to 720-1100 clock cycles on
a Sandy Bridge Xeon host, compared to 2300-3200 before the whole series
and 925-1700 after the first two low-hanging fruit changes.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2014-05-13 14:02:13 +02:00
parent 719d5a9b24
commit 44583cba91
1 changed files with 19 additions and 4 deletions
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23
arch/x86/kvm/x86.c
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@ -4085,7 +4085,8 @@ static int kvm_read_guest_virt_helper(gva_t addr, void *val, unsigned int bytes,
if (gpa == UNMAPPED_GVA)
return X86EMUL_PROPAGATE_FAULT;
ret = kvm_read_guest(vcpu->kvm, gpa, data, toread);
ret = kvm_read_guest_page(vcpu->kvm, gpa >> PAGE_SHIFT, data,
offset, toread);
if (ret < 0) {
r = X86EMUL_IO_NEEDED;
goto out;
@ -4106,10 +4107,24 @@ static int kvm_fetch_guest_virt(struct x86_emulate_ctxt *ctxt,
{
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0;
unsigned offset;
int ret;
return kvm_read_guest_virt_helper(addr, val, bytes, vcpu,
access | PFERR_FETCH_MASK,
exception);
/* Inline kvm_read_guest_virt_helper for speed. */
gpa_t gpa = vcpu->arch.walk_mmu->gva_to_gpa(vcpu, addr, access|PFERR_FETCH_MASK,
exception);
if (unlikely(gpa == UNMAPPED_GVA))
return X86EMUL_PROPAGATE_FAULT;
offset = addr & (PAGE_SIZE-1);
if (WARN_ON(offset + bytes > PAGE_SIZE))
bytes = (unsigned)PAGE_SIZE - offset;
ret = kvm_read_guest_page(vcpu->kvm, gpa >> PAGE_SHIFT, val,
offset, bytes);
if (unlikely(ret < 0))
return X86EMUL_IO_NEEDED;
return X86EMUL_CONTINUE;
}
int kvm_read_guest_virt(struct x86_emulate_ctxt *ctxt,