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Commit 44583cba authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: x86: use kvm_read_guest_page for emulator accesses 



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: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 719d5a9b

arch/x86/kvm/x86.c

+19 −4
Original line number Diff line number Diff line
@@ -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,

	/* 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,