linux-kernel - Re: [PATCH] KVM: x86: VMX: Make smaller physical guest address space support user-configurable

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Message-ID: <68a67f54-af5c-8b33-6b87-a67ccbbfc155@redhat.com>
Date:   Fri, 2 Oct 2020 19:30:56 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     Qian Cai <cai@...hat.com>, Mohammed Gamal <mgamal@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        lkft-triage@...ts.linaro.org
Subject: Re: [PATCH] KVM: x86: VMX: Make smaller physical guest address space
 support user-configurable

On 02/10/20 19:28, Naresh Kamboju wrote:
>>
>> commit 608e2791d7353e7d777bf32038ca3e7d548155a4 (HEAD -> kvm-master)
>> Author: Paolo Bonzini <pbonzini@...hat.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.
> 

Thanks, the issue with my disk is gone too so it'll get to Linus in time
for rc8.

Paolo