Messages in this thread Patch in this message | | | Subject | Re: [PATCH v2] KVM: x86: Avoid guest page table walk when gpa_available is set | From | Brijesh Singh <> | Date | Tue, 8 Aug 2017 14:24:59 -0500 |
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Hi Radim,
On 07/20/2017 02:43 AM, Radim Krčmář wrote: > 2017-07-19 08:35-0500, Brijesh Singh: >> On 07/19/2017 06:19 AM, Radim Krčmář wrote: >>> 2017-07-17 16:32-0500, Brijesh Singh: >>>> Hi Paolo and Radim >>>> >>>> Any comments on this patch, I could not find it in 4.13-2 branch. >>>> >>>> Please let me know if you want to fix something, or want me to >>>> refresh and resend the patch. >>> >>> Sorry, I tried it during the merge window, but it didn't pass tests on >>> VMX and I got distracted by other bugs before looking into the cause. >>> >>> Can you reproduce the fail? >>> >> >> No worries, thanks. >> >> I can try to reproduce it, are you running kvm-unittest or something different? > > I noticed that a linux guest hung in early boot, but at least (io)apic > kvm-unit-tests failed as well, IIRC. > >> IIRC, VMX does not set the gpa_available flag hence I am wondering what did I miss >> in the patch to trigger the failure. I will debug it and let you know. > > It does now, in ept_violation and ept_misconfig, >
I am able to reproduce the issue on VMX, Sorry it took a bit longer to verify it.
I was not aware that VMX is also making use of gpa_available flag hence I missed updating the vmx.c to set the gpa_val. After applying the below small patch I am able to boot the guest on Intel Xeon E5-2665.
Additionally, there was one issue in current patch pointed by Paolo [1]. If patch was using vcpu->arch.gpa_val check as pointed by Paolo then on VMX we will silently fallback to guest page table walk (even when gpa_available is set). I guess since I have testing my code on SVM platform hence never caught the error. I will soon send updated patch.
[1] http://marc.info/?l=kvm&m=150116338725964&w=2
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index b5e0b02..9309fbb 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6309,6 +6309,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu) ? PFERR_PRESENT_MASK : 0; vcpu->arch.gpa_available = true; + vcpu->arch.gpa_val = gpa; vcpu->arch.exit_qualification = exit_qualification; return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0); @@ -6326,6 +6327,7 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu) } ret = handle_mmio_page_fault(vcpu, gpa, true); + vcpu->arch.gpa_val = gpa; vcpu->arch.gpa_available = true; if (likely(ret == RET_MMIO_PF_EMULATE)) return x86_emulate_instruction(vcpu, gpa, 0, NULL, 0) ==
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