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@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 905edf8557e7..f750b69ca443 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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,
--
1.8.3.1
--
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