From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Junaid Shahid <junaids@google.com>
Subject: Re: [PATCH v2 0/8] KVM: x86/mmu: ITLB multi-hit workaround fixes
Date: Fri, 25 Sep 2020 23:27:15 +0200 [thread overview]
Message-ID: <4eec29f9-def0-3292-4a88-1f6ff3e06b5e@redhat.com> (raw)
In-Reply-To: <20200923183735.584-1-sean.j.christopherson@intel.com>
On 23/09/20 20:37, Sean Christopherson wrote:
> Patch 1 is a minor fix for a very theoretical bug where KVM could skip
> the final "commit zap" when recovering shadow pages for the NX huge
> page mitigation.
>
> Patch 2 is cleanup that's made possible by patch 1.
>
> Patches 3-5 are the main course and fix bugs in the NX huge page
> accounting where shadow pages are incorrectly added to the list of
> disallowed huge pages. KVM doesn't actually check to see if the page
> could actually have been a large page when adding to the disallowed list.
> This result in what are effectively spurious zaps. The biggest issue is
> likely with shadow pages in the upper levels, i.e. levels 3 and 4, as they
> are either unlikely to be huge (1gb) or flat out can't be huge (512tb).
> And because of the way KVM zaps, the upper levels will be zapped first,
> i.e. KVM is likely zapping and rebuilding a decent number of its shadow
> pages for zero benefit.
>
> Ideally, patches 3-5 would be a single patch to ease backporting. In the
> end, I decided the change is probably not suitable for stable as at worst
> it creates an infrequent performance spike (assuming the admin isn't going
> crazy with the recovery frequency), and it's far from straightforward or
> risk free. Cramming everything into a single patch was a mess.
>
> Patches 6-8 are cleanups in related code. The 'hlevel' name in particular
> has been on my todo list for a while.
>
> v2:
> - Rebased to kvm/queue, commit e1ba1a15af73 ("KVM: SVM: Enable INVPCID
> feature on AMD").
>
> Sean Christopherson (8):
> KVM: x86/mmu: Commit zap of remaining invalid pages when recovering
> lpages
> KVM: x86/mmu: Refactor the zap loop for recovering NX lpages
> KVM: x86/mmu: Move "huge page disallowed" calculation into mapping
> helpers
> KVM: x86/mmu: Capture requested page level before NX huge page
> workaround
> KVM: x86/mmu: Account NX huge page disallowed iff huge page was
> requested
> KVM: x86/mmu: Rename 'hlevel' to 'level' in FNAME(fetch)
> KVM: x86/mmu: Hoist ITLB multi-hit workaround check up a level
> KVM: x86/mmu: Track write/user faults using bools
>
> arch/x86/kvm/mmu/mmu.c | 58 +++++++++++++++++++++-------------
> arch/x86/kvm/mmu/paging_tmpl.h | 39 ++++++++++++-----------
> 2 files changed, 57 insertions(+), 40 deletions(-)
>
Queued, thanks.
Paolo
prev parent reply other threads:[~2020-09-25 21:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 18:37 [PATCH v2 0/8] KVM: x86/mmu: ITLB multi-hit workaround fixes Sean Christopherson
2020-09-23 18:37 ` [PATCH v2 1/8] KVM: x86/mmu: Commit zap of remaining invalid pages when recovering lpages Sean Christopherson
2020-09-23 18:37 ` [PATCH v2 4/8] KVM: x86/mmu: Capture requested page level before NX huge page workaround Sean Christopherson
2020-09-23 18:37 ` [PATCH v2 5/8] KVM: x86/mmu: Account NX huge page disallowed iff huge page was requested Sean Christopherson
2020-09-23 18:37 ` [PATCH v2 6/8] KVM: x86/mmu: Rename 'hlevel' to 'level' in FNAME(fetch) Sean Christopherson
2020-09-25 21:25 ` Paolo Bonzini
2020-09-23 18:37 ` [PATCH v2 7/8] KVM: x86/mmu: Hoist ITLB multi-hit workaround check up a level Sean Christopherson
2020-09-23 18:37 ` [PATCH v2 8/8] KVM: x86/mmu: Track write/user faults using bools Sean Christopherson
2020-09-25 21:27 ` Paolo Bonzini [this message]
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