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DIR:OUT; SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?OGkKG0ljQNkJXLnuz3O2vr9U0rswy/xmBd5cgOyiyMo1VUp6l3kTzZpV6N1b?= =?us-ascii?Q?Oj90H5Ap15c1h0y9J9e26OxxUtZWDKrgez/HTxz8QBtDDVIInrRka+qC1Jh6?= =?us-ascii?Q?AgQX6d/2kg0gXEq+WAQAx+DwCHGPfGuD5qDRdiZxLOZe9GWQCsPdwuXZET/O?= =?us-ascii?Q?4KfqdBgJcnTdNLSj/XoGttWIudH3/0sP0gYfcuztHBvKnwCkOVH0eK9HWFg5?= =?us-ascii?Q?a0OroxuBjVClFpiOtXtes4ISsqJM+yw4/Ns8kpaDDKREteppmGWOUyZC1hRK?= =?us-ascii?Q?zxew2GjDbWpCkT4h43RP6PFzKQKOwBW7jrwEOs8QgVGellVxnV8/ApEUWKkh?= =?us-ascii?Q?aQH6nVyxKhvY2YXFR22LTURAyRQhQvQ4ggUOqdShsDs+3cmLjLn3R6LaIB/V?= =?us-ascii?Q?8aHsVXDPQHEagd8Cop5WK6X8XADuQw3RrXN+swRezIFM3bdow+Q4yJ7Q0rp2?= =?us-ascii?Q?GOfKtBZ2EP0UVrQ+K/Sj9kkiTn6kMuWxI3ACvojQ0Dft6v0FZnApG58WEAmR?= =?us-ascii?Q?yIbf4B4Qx5yU/uQ7J9u8kO0uR8RnshZ7xifXyMrYBOXTGHAbnQsnlmTqJFwK?= =?us-ascii?Q?b40/y4QhFQnobH5arm+0KKA4oJc6dhMA4jcu20YyJ9RfILco0tpW4fWAhCWc?= =?us-ascii?Q?+Qx3HxRZfoDu0StgGIuhEU4Um3OXetQY88bk23WGd8D87VCrSy3Avdt3iiat?= =?us-ascii?Q?6l2NuvS4EDQ5nD8Z7JFjSf/4iMjMOmsIfmQrxwsDb98kFlooNyHVBbYgYsBD?= =?us-ascii?Q?aP1WTFhn+/sQRiLiBKBJ1ojENfnmbOvFzFIrpcES7I9+qM4Ua6HDgzWV09Hg?= =?us-ascii?Q?YaQAVyBroiPkPC3ZELZWWM3QqXt3sZ5Gi24zVKhS7u2yV9b0HXeRUJ03Jjg/?= =?us-ascii?Q?s+HGl+B1qkej7rTdr6wNkKydVvvHlUG4slzlFYS0qi0bmob5c3x9iMoATidV?= =?us-ascii?Q?IjnBBIsA4cODF3byOlMLIDzBhYQnyRJOL7pcQwjuRf4VDirY/Tw7aztRYG2F?= =?us-ascii?Q?AxhwaMyFVS9FkoWfHvUONHseWwJ1U/5UTIvSLkcyMPYqrDw5YDMGrpBaZE9x?= =?us-ascii?Q?Yl3+uk4K1vWO1sI66RBXUL6JqANDmwc4eHSuWI1lboYu9yAH+K2IO+QKevTj?= =?us-ascii?Q?UCKYryVh4oXHpwn2MfzTW0Rp20DE2Ur034Eyrtsl6Q86coBrnCrm7FwxuK4q?= =?us-ascii?Q?u0qiZjpmju/p4jM1MR2FVS/NXheOWquCv0D+RJi5JkxgTSfnHdiAkpSvKwL3?= =?us-ascii?Q?GGdPt9t4aqQUvVTUloojFWyBmqUUYclOMCmPx4PCn1bcydahLdn2kb95kSZF?= =?us-ascii?Q?hLb1dhw5jBD08X/eu9GHt21bsUV3drThFLjpa4cyEhH1JtHUNe/nTALeKr6v?= =?us-ascii?Q?kwce7PCuZ2KCta60UnqYm63eUyAaDnDAl87hrnYKBvtE59ix3Ope3vc6/VUQ?= =?us-ascii?Q?rNzQFoAc5uZEit/3qs+haauGTtYQLQb/sptB/+BXMyGCFFR3lwCjrXQsWz9e?= =?us-ascii?Q?lfAXLVKuGjt/U/P/AEdC0VVmB68s2O/i62iUpYNyKuSR4eQwKcxW/b1N4Z9d?= =?us-ascii?Q?ILhKimuYtcvWOHC+O5iETNqJI16ej5LFtnVVQJGN?= X-MS-Exchange-CrossTenant-Network-Message-Id: e121b4f4-fcf4-4bfd-8dfb-08db99331070 X-MS-Exchange-CrossTenant-AuthSource: DS7PR11MB5966.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Aug 2023 23:48:00.6107 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: l8bkJDqtkjrZXhxC+5OIy583Nb1krETQtCm7w8tVhnevdu9MmbRgX2XPSfanXxO3njw6EilnFpw0fLZiHHOcOw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR11MB7901 X-OriginatorOrg: intel.com Subject: Re: [Intel-gfx] [PATCH 19/27] KVM: x86/mmu: Use page-track notifiers iff there are external users X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Yan Zhao Cc: Like Xu , kvm@vger.kernel.org, intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, Ben Gardon , Paolo Bonzini , intel-gvt-dev@lists.freedesktop.org Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Wed, Aug 09, 2023 at 07:33:45AM -0700, Sean Christopherson wrote: > On Wed, Aug 09, 2023, Yan Zhao wrote: > > On Mon, Aug 07, 2023 at 10:19:07AM -0700, Sean Christopherson wrote: > > > On Mon, Aug 07, 2023, Like Xu wrote: > > > > On 23/12/2022 8:57 am, Sean Christopherson wrote: > > > > > +static inline void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, > > > > > + const u8 *new, int bytes) > > > > > +{ > > > > > + __kvm_page_track_write(vcpu, gpa, new, bytes); > > > > > + > > > > > + kvm_mmu_track_write(vcpu, gpa, new, bytes); > > > > > +} > > > > > > > > The kvm_mmu_track_write() is only used for x86, where the incoming parameter > > > > "u8 *new" has not been required since 0e0fee5c539b ("kvm: mmu: Fix race in > > > > emulated page table writes"), please help confirm if it's still needed ? Thanks. > > > > A minor clean up is proposed. > > > > > > Hmm, unless I'm misreading things, KVMGT ultimately doesn't consume @new either. > > > So I think we can remove @new from kvm_page_track_write() entirely. > > Sorry for the late reply. > > Yes, KVMGT does not consume @new and it reads the guest PTE again in the > > page track write handler. > > > > But I have a couple of questions related to the memtioned commit as > > below: > > > > (1) If "re-reading the current value of the guest PTE after the MMU lock has > > been acquired", then should KVMGT also acquire the MMU lock too? > > No. If applicable, KVMGT should read the new/current value after acquiring > whatever lock protects the generation (or update) of the shadow entries. I > suspect KVMGT already does this, but I don't have time to confirm that at this I think the mutex lock and unlock of info->vgpu_lock you added in kvmgt_page_track_write() is the counterpart :) > exact memory. > > The race that was fixed in KVM was: > > vCPU0 vCPU1 > write X > write Y > sync SPTE w/ Y > sync SPTE w/ X > > Reading the value after acquiring mmu_lock ensures that both vCPUs will see whatever > value "loses" the race, i.e. whatever written value is processed second ('Y' in the > above sequence). I suspect that vCPU0 may still generate a wrong SPTE if vCPU1 wrote 4 bytes while vCPU0 wrote 8 bytes, though the chances are very low. > > > If so, could we move the MMU lock and unlock into kvm_page_track_write() > > as it's common. > > > > (2) Even if KVMGT consumes @new, > > will kvm_page_track_write() be called for once or twice if there are two > > concurent emulated write? > > Twice, kvm_page_track_write() is wired up directly to the emulation of the write, > i.e. there is no batching.