From: Naresh Kamboju <naresh.kamboju@linaro.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Qian Cai <cai@redhat.com>, Mohammed Gamal <mgamal@redhat.com>,
kvm list <kvm@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Linux-Next Mailing List <linux-next@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
lkft-triage@lists.linaro.org
Subject: Re: [PATCH] KVM: x86: VMX: Make smaller physical guest address space support user-configurable
Date: Fri, 2 Oct 2020 22:58:53 +0530 [thread overview]
Message-ID: <CA+G9fYvm1Ux7XmmXgpPHmLJ4WbRoPowbEfbub1HC2G4E-1r-1g@mail.gmail.com> (raw)
In-Reply-To: <c385b225-77fb-cf2a-fba3-c70a9b6d541d@redhat.com>
Hi Paolo,
Thanks for the patch.
On Tue, 29 Sep 2020 at 20:17, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 29/09/20 15:39, Qian Cai wrote:
> > On Tue, 2020-09-29 at 14:26 +0200, Paolo Bonzini wrote:
> >> On 29/09/20 13:59, Qian Cai wrote:
> >>> WARN_ON_ONCE(!allow_smaller_maxphyaddr);
> >>>
> >>> I noticed the origin patch did not have this WARN_ON_ONCE(), but the
> >>> mainline
> >>> commit b96e6506c2ea ("KVM: x86: VMX: Make smaller physical guest address
> >>> space
> >>> support user-configurable") does have it for some reasons.
> >>
> >> Because that part of the code should not be reached. The exception
> >> bitmap is set up with
> >>
> >> if (!vmx_need_pf_intercept(vcpu))
> >> eb &= ~(1u << PF_VECTOR);
> >>
> >> where
> >>
> >> static inline bool vmx_need_pf_intercept(struct kvm_vcpu *vcpu)
> >> {
> >> if (!enable_ept)
> >> return true;
> >>
> >> return allow_smaller_maxphyaddr &&
> >> cpuid_maxphyaddr(vcpu) < boot_cpu_data.x86_phys_bits;
> >> }
> >>
> >> We shouldn't get here if "enable_ept && !allow_smaller_maxphyaddr",
> >> which implies vmx_need_pf_intercept(vcpu) == false. So the warning is
> >> genuine; I've sent a patch.
> >
> > Care to provide a link to the patch? Just curious.
> >
>
> Ok, I haven't sent it yet. :) But here it is:
>
> commit 608e2791d7353e7d777bf32038ca3e7d548155a4 (HEAD -> kvm-master)
> Author: Paolo Bonzini <pbonzini@redhat.com>
> Date: Tue Sep 29 08:31:32 2020 -0400
>
> KVM: VMX: update PFEC_MASK/PFEC_MATCH together with PF intercept
>
> The PFEC_MASK and PFEC_MATCH fields in the VMCS reverse the meaning of
> the #PF intercept bit in the exception bitmap when they do not match.
> This means that, if PFEC_MASK and/or PFEC_MATCH are set, the
> hypervisor can get a vmexit for #PF exceptions even when the
> corresponding bit is clear in the exception bitmap.
>
> This is unexpected and is promptly reported as a WARN_ON_ONCE.
> To fix it, reset PFEC_MASK and PFEC_MATCH when the #PF intercept
> is disabled (as is common with enable_ept && !allow_smaller_maxphyaddr).
I have tested this patch on an x86_64 machine and the reported issue is gone.
>
> Reported-by: Qian Cai <cai@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index f0384e93548a..f4e9c310032a 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -794,6 +794,18 @@ void update_exception_bitmap(struct kvm_vcpu *vcpu)
> */
> if (is_guest_mode(vcpu))
> eb |= get_vmcs12(vcpu)->exception_bitmap;
> + else {
> + /*
> + * If EPT is enabled, #PF is only trapped if MAXPHYADDR is mismatched
> + * between guest and host. In that case we only care about present
> + * faults. For vmcs02, however, PFEC_MASK and PFEC_MATCH are set in
> + * prepare_vmcs02_rare.
> + */
> + bool selective_pf_trap = enable_ept && (eb & (1u << PF_VECTOR));
> + int mask = selective_pf_trap ? PFERR_PRESENT_MASK : 0;
> + vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, mask);
> + vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, mask);
> + }
>
> vmcs_write32(EXCEPTION_BITMAP, eb);
> }
> @@ -4355,16 +4367,6 @@ static void init_vmcs(struct vcpu_vmx *vmx)
> vmx->pt_desc.guest.output_mask = 0x7F;
> vmcs_write64(GUEST_IA32_RTIT_CTL, 0);
> }
> -
> - /*
> - * If EPT is enabled, #PF is only trapped if MAXPHYADDR is mismatched
> - * between guest and host. In that case we only care about present
> - * faults.
> - */
> - if (enable_ept) {
> - vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, PFERR_PRESENT_MASK);
> - vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, PFERR_PRESENT_MASK);
> - }
> }
>
> static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>
test log link
https://lkft.validation.linaro.org/scheduler/job/1813223
- Naresh
next prev parent reply other threads:[~2020-10-02 17:29 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-03 14:11 [PATCH] KVM: x86: VMX: Make smaller physical guest address space support user-configurable Mohammed Gamal
2020-09-03 17:57 ` Jim Mattson
2020-09-03 18:03 ` Paolo Bonzini
2020-09-03 18:32 ` Jim Mattson
2020-09-03 20:02 ` Paolo Bonzini
2020-09-03 21:26 ` Jim Mattson
2020-09-23 13:45 ` Paolo Bonzini
[not found] ` <CALMp9eTHbhwfdq4Be=XcUG9z82KK8AapQeVmsdH=mGdQ_Yt2ug@mail.gmail.com>
2020-09-23 15:19 ` Paolo Bonzini
2020-09-28 15:34 ` Qian Cai
2020-09-29 11:59 ` Qian Cai
2020-09-29 12:26 ` Paolo Bonzini
2020-09-29 13:39 ` Qian Cai
2020-09-29 14:47 ` Paolo Bonzini
2020-10-02 17:28 ` Naresh Kamboju [this message]
2020-10-02 17:30 ` Paolo Bonzini
2021-01-16 0:08 ` Jim Mattson
2021-01-18 10:18 ` Mohammed Gamal
2021-06-21 18:01 ` Jim Mattson
2021-06-22 12:59 ` Mohammed Gamal
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