From: Sean Christopherson <seanjc@google.com>
To: Michael Roth <michael.roth@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-coco@lists.linux.dev,
linux-mm@kvack.org, linux-crypto@vger.kernel.org,
x86@kernel.org, linux-kernel@vger.kernel.org,
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vkuznets@redhat.com, jmattson@google.com, luto@kernel.org,
dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com,
peterz@infradead.org, srinivas.pandruvada@linux.intel.com,
rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com,
bp@alien8.de, vbabka@suse.cz, kirill@shutemov.name,
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jarkko@kernel.org, ashish.kalra@amd.com,
nikunj.dadhania@amd.com, pankaj.gupta@amd.com,
liam.merwick@oracle.com, papaluri@amd.com,
Isaku Yamahata <isaku.yamahata@intel.com>
Subject: Re: [PATCH v15 21/23] KVM: MMU: Disable fast path for private memslots
Date: Fri, 10 May 2024 08:59:09 -0700 [thread overview]
Message-ID: <Zj5ETYPTUo9T4Nuf@google.com> (raw)
In-Reply-To: <20240510152744.ejdy4jqawc2zd2dt@amd.com>
On Fri, May 10, 2024, Michael Roth wrote:
> On Fri, May 10, 2024 at 03:50:26PM +0200, Paolo Bonzini wrote:
> > On Fri, May 10, 2024 at 3:47 PM Sean Christopherson <seanjc@google.com> wrote:
> > >
> > > > + * Since software-protected VMs don't have a notion of a shared vs.
> > > > + * private that's separate from what KVM is tracking, the above
> > > > + * KVM_EXIT_MEMORY_FAULT condition wouldn't occur, so avoid the
> > > > + * special handling for that case for now.
> > >
> > > Very technically, it can occur if userspace _just_ modified the attributes. And
> > > as I've said multiple times, at least for now, I want to avoid special casing
> > > SW-protected VMs unless it is *absolutely* necessary, because their sole purpose
> > > is to allow testing flows that are impossible to excercise without SNP/TDX hardware.
> >
> > Yep, it is not like they have to be optimized.
>
> Ok, I thought there were maybe some future plans to use sw-protected VMs
> to get some added protections from userspace. But even then there'd
> probably still be extra considerations for how to handle access tracking
> so white-listing them probably isn't right anyway.
>
> I was also partly tempted to take this route because it would cover this
> TDX patch as well:
>
> https://lore.kernel.org/lkml/91c797997b57056224571e22362321a23947172f.1705965635.git.isaku.yamahata@intel.com/
Hmm, I'm pretty sure that patch is trying to fix the exact same issue you are
fixing, just in a less precise way. S-EPT entries only support RWX=0 and RWX=111b,
i.e. it should be impossible to have a write-fault to a present S-EPT entry.
And if TDX is running afoul of this code:
if (!fault->present)
return !kvm_ad_enabled();
then KVM should do the sane thing and require A/D support be enabled for TDX.
And if it's something else entirely, that changelog has some explaining to do.
> and avoid any weirdness about checking kvm_mem_is_private() without
> checking mmu_invalidate_seq, but I think those cases all end up
> resolving themselves eventually and added some comments around that.
Yep, checking state that is protected by mmu_invalidate_seq outside of mmu_lock
is definitely allowed, e.g. the entire fast page fault path operates outside of
mmu_lock and thus outside of mmu_invalidate_seq's purview.
It's a-ok because the SPTE are done with an atomic CMPXCHG, and so KVM only needs
to ensure its page tables aren't outright _freed_. If the zap triggered by the
attributes change "wins", then the fast #PF path will fail the CMPXCHG and be an
expensive NOP. If the fast #PF wins, the zap will pave over the fast #PF fix,
and the IPI+flush that is needed for all zaps, to ensure vCPUs don't have stale
references, does the rest.
And if there's an attributes race that causes the fast #PF to bail early, the vCPU
will see the correct state on the next page fault.
next prev parent reply other threads:[~2024-05-10 15:59 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-01 8:51 [PATCH v15 00/20] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Michael Roth
2024-05-01 8:51 ` [PATCH v15 01/20] Revert "KVM: x86: Add gmem hook for determining max NPT mapping level" Michael Roth
2024-05-01 8:51 ` [PATCH v15 02/20] KVM: x86: Add hook for determining max NPT mapping level Michael Roth
2024-05-02 23:11 ` Isaku Yamahata
2024-05-07 17:48 ` Paolo Bonzini
2024-05-01 8:51 ` [PATCH v15 03/20] KVM: SEV: Select KVM_GENERIC_PRIVATE_MEM when CONFIG_KVM_AMD_SEV=y Michael Roth
2024-05-01 8:51 ` [PATCH v15 04/20] KVM: SEV: Add initial SEV-SNP support Michael Roth
2024-05-01 8:51 ` [PATCH v15 05/20] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_START command Michael Roth
2024-05-01 8:51 ` [PATCH v15 06/20] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_UPDATE command Michael Roth
2024-05-01 8:51 ` [PATCH v15 07/20] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_FINISH command Michael Roth
2024-05-01 8:51 ` [PATCH v15 08/20] KVM: SEV: Add support to handle GHCB GPA register VMGEXIT Michael Roth
2024-05-01 8:51 ` [PATCH v15 09/20] KVM: SEV: Add support to handle MSR based Page State Change VMGEXIT Michael Roth
2024-05-16 8:28 ` Binbin Wu
2024-05-16 17:23 ` Paolo Bonzini
2024-05-21 0:49 ` Binbin Wu
2024-05-21 21:49 ` Michael Roth
2024-05-27 12:25 ` Binbin Wu
2024-05-28 10:39 ` Paolo Bonzini
2024-05-29 20:02 ` Sean Christopherson
2024-05-31 1:22 ` Binbin Wu
2024-05-31 13:10 ` Paolo Bonzini
2024-05-30 16:47 ` Zhi Wang
2024-05-01 8:52 ` [PATCH v15 10/20] KVM: SEV: Add support to handle " Michael Roth
2024-05-01 8:52 ` [PATCH v15 11/20] KVM: SEV: Add support to handle RMP nested page faults Michael Roth
2024-05-01 8:52 ` [PATCH v15 12/20] KVM: SEV: Support SEV-SNP AP Creation NAE event Michael Roth
2024-05-01 8:52 ` [PATCH v15 13/20] KVM: SEV: Implement gmem hook for initializing private pages Michael Roth
2024-05-20 10:16 ` Huang, Kai
2024-05-20 17:35 ` Sean Christopherson
2024-05-20 21:57 ` Huang, Kai
2024-05-20 23:15 ` Sean Christopherson
2024-05-20 23:41 ` Huang, Kai
2024-05-21 0:30 ` Sean Christopherson
2024-05-20 19:14 ` Isaku Yamahata
2024-05-01 8:52 ` [PATCH v15 14/20] KVM: SEV: Implement gmem hook for invalidating " Michael Roth
2024-05-01 8:52 ` [PATCH v15 15/20] KVM: x86: Implement hook for determining max NPT mapping level Michael Roth
2024-05-01 8:52 ` [PATCH v15 16/20] KVM: SEV: Avoid WBINVD for HVA-based MMU notifications for SNP Michael Roth
2024-05-01 8:52 ` [PATCH v15 17/20] KVM: SVM: Add module parameter to enable SEV-SNP Michael Roth
2024-05-01 8:52 ` [PATCH v15 18/20] KVM: SEV: Provide support for SNP_GUEST_REQUEST NAE event Michael Roth
2024-05-01 8:52 ` [PATCH v15 19/20] KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST " Michael Roth
2024-05-13 23:48 ` Sean Christopherson
2024-05-14 2:51 ` Michael Roth
2024-05-14 14:36 ` Sean Christopherson
2024-05-15 1:25 ` [PATCH] KVM: SEV: Replace KVM_EXIT_VMGEXIT with KVM_EXIT_SNP_REQ_CERTS Michael Roth
2024-05-01 8:52 ` [PATCH v15 20/20] crypto: ccp: Add the SNP_VLEK_LOAD command Michael Roth
2024-05-07 18:04 ` [PATCH v15 00/20] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Paolo Bonzini
2024-05-07 18:14 ` Michael Roth
2024-05-10 2:34 ` Michael Roth
2024-05-10 1:58 ` [PATCH v15 21/23] KVM: MMU: Disable fast path for private memslots Michael Roth
2024-05-10 1:58 ` [PATCH v15 22/23] KVM: SEV: Fix return code interpretation for RMP nested page faults Michael Roth
2024-05-10 13:58 ` Sean Christopherson
2024-05-10 15:36 ` Michael Roth
2024-05-10 16:01 ` Paolo Bonzini
2024-05-10 16:37 ` Michael Roth
2024-05-10 16:59 ` Paolo Bonzini
2024-05-10 17:25 ` Paolo Bonzini
2024-05-14 8:10 ` Borislav Petkov
2024-05-10 1:58 ` [PATCH v15 23/23] KVM: SEV: Fix PSC handling for SMASH/UNSMASH and partial update ops Michael Roth
2024-05-10 17:09 ` Paolo Bonzini
2024-05-10 19:08 ` Michael Roth
2024-05-10 13:47 ` [PATCH v15 21/23] KVM: MMU: Disable fast path for private memslots Sean Christopherson
2024-05-10 13:50 ` Paolo Bonzini
2024-05-10 15:27 ` Michael Roth
2024-05-10 15:59 ` Sean Christopherson [this message]
2024-05-10 17:47 ` Isaku Yamahata
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