Alexander Graf wrote:
Until this patch we bounced between the VM and the VMM for a couple of
instructions after CLGI, only to find out that yet another SVM instruction
follows.
Since roundtrips are really expensive, it's a lot faster to emulate these
few instructions. Now we can execute CLGI/VMLOAD/VMRUN on one intercept and
VMEXIT/VMSAVE on another. This is a major speed improvement!
Neat trick. Have you looked at svm.c to see if we can cut out
extraneous instructions (or move them out of the gif=0 area)? Could
mean big savings.
+static int nested_svm_emulate(struct vcpu_svm *svm, struct kvm_run *kvm_run)
+{
+ int er;
+ u32 opcode = 0;
+ unsigned long rip;
+ unsigned long rip_linear;
+
+ svm->vmcb->save.rax = svm->vcpu.arch.regs[VCPU_REGS_RAX];
+ svm->vmcb->save.rsp = svm->vcpu.arch.regs[VCPU_REGS_RSP];
+ svm->vmcb->save.rip = svm->vcpu.arch.regs[VCPU_REGS_RIP];
+ rip = svm->vcpu.arch.regs[VCPU_REGS_RIP];
+ rip_linear = rip + svm_seg(&svm->vcpu, VCPU_SREG_CS)->base;
+
+ er = emulator_read_std(rip_linear, (void *)&opcode, 3, &svm->vcpu);
+ if (er != X86EMUL_CONTINUE)
+ return er;
+ er = EMULATE_FAIL;
+
+ switch (opcode) {
+ case 0xda010f:
+ vmload_interception(svm, kvm_run);
+ er = EMULATE_DONE;
+ break;
+ case 0xd8010f:
+ vmrun_interception(svm, kvm_run);
+ er = EMULATE_DONE;
+ break;
+ case 0xdb010f:
+ vmsave_interception(svm, kvm_run);
+ er = EMULATE_DONE;
+ break;
+ case 0xdc010f:
+ stgi_interception(svm, kvm_run);
+ er = EMULATE_DONE;
+ break;
+ default:
+ nsvm_printk("NSVM: Opcode %x unknown\n", opcode);
+ }
+
+ nsvm_printk("NSVM: svm emul at 0x%lx -> %d\n", rip, er);
+
+ return er;
+}
+
Move to the regular x86 emulator, so if we extend it with debug flag
support, privilege checking, etc, we get that for svm as well.
static int nested_svm_vmexit_real(struct vcpu_svm *svm, void *arg1,
void *arg2, void *opaque)
{
@@ -1551,6 +1600,9 @@ static int nested_svm_vmexit(struct vcpu_svm *svm)
kvm_mmu_reset_context(&svm->vcpu);
kvm_mmu_load(&svm->vcpu);
+ /* KVM calls vmsave after vmrun, so let's run it now if we can */
+ nested_svm_emulate(svm, NULL);
+
Will also call stgi eventually, so it may make sense to loop here too.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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