From: Paolo Bonzini <pbonzini@redhat.com>
To: Tom Lendacky <thomas.lendacky@amd.com>,
Mohammed Gamal <mgamal@redhat.com>,
kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, vkuznets@redhat.com,
sean.j.christopherson@intel.com, wanpengli@tencent.com,
jmattson@google.com, joro@8bytes.org, babu.moger@amd.com
Subject: Re: [PATCH v2 00/11] KVM: Support guest MAXPHYADDR < host MAXPHYADDR
Date: Sat, 20 Jun 2020 01:07:49 +0200 [thread overview]
Message-ID: <52295811-f78a-46c5-ff9e-23709ba95a3d@redhat.com> (raw)
In-Reply-To: <5a52fd65-e1b2-ca87-e923-1d5ac167cfb9@amd.com>
On 19/06/20 23:52, Tom Lendacky wrote:
>> A more subtle issue is when the host MAXPHYADDR is larger than that
>> of the guest. Page faults caused by reserved bits on the guest won't
>> cause an EPT violation/NPF and hence we also check guest MAXPHYADDR
>> and add PFERR_RSVD_MASK error code to the page fault if needed.
>
> I'm probably missing something here, but I'm confused by this
> statement. Is this for a case where a page has been marked not
> present and the guest has also set what it believes are reserved
> bits? Then when the page is accessed, the guest sees a page fault
> without the error code for reserved bits?
No, for non-present page there is no issue because there are no reserved
bits in that case. If the page is present and no reserved bits are set
according to the host, however, there are two cases to consider:
- if the page is not accessible to the guest according to the
permissions in the page table, it will cause a #PF. We need to trap it
and change the error code into P|RSVD if the guest physical address has
any guest-reserved bits.
- if the page is accessible to the guest according to the permissions in
the page table, it will cause a #NPF. Again, we need to trap it, check
the guest physical address and inject a P|RSVD #PF if the guest physical
address has any guest-reserved bits.
The AMD specific issue happens in the second case. By the time the NPF
vmexit occurs, the accessed and/or dirty bits have been set and this
should not have happened before the RSVD page fault that we want to
inject. On Intel processors, instead, EPT violations trigger before
accessed and dirty bits are set. I cannot find an explicit mention of
the intended behavior in either the
Intel SDM or the AMD APM.
Paolo
next prev parent reply other threads:[~2020-06-19 23:07 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-19 15:39 [PATCH v2 00/11] KVM: Support guest MAXPHYADDR < host MAXPHYADDR Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 01/11] KVM: x86: Add helper functions for illegal GPA checking and page fault injection Mohammed Gamal
2020-06-22 4:44 ` Yuan Yao
2020-06-22 12:21 ` Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 02/11] KVM: x86: mmu: Move translate_gpa() to mmu.c Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 03/11] KVM: x86: mmu: Add guest physical address check in translate_gpa() Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 04/11] KVM: x86: rename update_bp_intercept to update_exception_bitmap Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 05/11] KVM: x86: update exception bitmap on CPUID changes Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 06/11] KVM: VMX: introduce vmx_need_pf_intercept Mohammed Gamal
2020-06-19 22:45 ` Jim Mattson
2020-06-22 13:57 ` Paolo Bonzini
2020-06-19 15:39 ` [PATCH v2 07/11] KVM: VMX: Add guest physical address check in EPT violation and misconfig Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 08/11] KVM: VMX: optimize #PF injection when MAXPHYADDR does not match Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 09/11] KVM: SVM: introduce svm_need_pf_intercept Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 10/11] KVM: SVM: Add guest physical address check in NPF/PF interception Mohammed Gamal
2020-06-19 15:39 ` [PATCH v2 11/11] KVM: x86: SVM: VMX: Make GUEST_MAXPHYADDR < HOST_MAXPHYADDR support configurable Mohammed Gamal
2020-06-19 15:43 ` [PATCH v2 00/11] KVM: Support guest MAXPHYADDR < host MAXPHYADDR Paolo Bonzini
2020-06-19 21:52 ` Tom Lendacky
2020-06-19 23:07 ` Paolo Bonzini [this message]
2020-06-22 16:33 ` Tom Lendacky
2020-06-22 17:03 ` Paolo Bonzini
2020-06-22 17:57 ` Tom Lendacky
2020-06-22 18:01 ` Paolo Bonzini
2020-06-22 19:14 ` Tom Lendacky
2020-06-22 22:20 ` Paolo Bonzini
2020-06-22 23:47 ` Andy Lutomirski
2020-06-23 0:52 ` Paolo Bonzini
2020-06-22 15:08 ` Mohammed Gamal
2020-06-22 15:23 ` Paolo Bonzini
2020-06-22 16:35 ` Tom Lendacky
2020-06-22 4:32 ` Yuan Yao
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