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([2001:b07:6468:f312:ec9b:111a:97e3:4baf]) by smtp.gmail.com with ESMTPSA id v2sm4072448wrm.16.2020.09.25.14.27.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Sep 2020 14:27:15 -0700 (PDT) Subject: Re: [PATCH v2 0/8] KVM: x86/mmu: ITLB multi-hit workaround fixes To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Junaid Shahid References: <20200923183735.584-1-sean.j.christopherson@intel.com> From: Paolo Bonzini Message-ID: <4eec29f9-def0-3292-4a88-1f6ff3e06b5e@redhat.com> Date: Fri, 25 Sep 2020 23:27:15 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200923183735.584-1-sean.j.christopherson@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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