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AJvYcCUd+SA3xTu+6OfJwl+ZQM3p+k0zTJpEbvPOk3+ISgw0OKdptw21Nw9lYKis4ShiQD+DFN88vXkjpQ==@kvack.org X-Gm-Message-State: AOJu0YyRfs8YTAgymjzMlx76WVJ7OR+K0zV1ms1LTHjwYOs+xZFrOOZk cBEFXgCkyAE91Rqca1Fa+DI10bIvewqgVkvVrjZCIY5Ls5vl91q+XY69TXSXGfNLoCRpHScXoam /vw== X-Google-Smtp-Source: AGHT+IGF8eBnjAYFXIPI8U2dRPCijHocf42fEz6xwJrtVSsRVB6bz3zjqLRx5gwWh1OyqfcDjPG12qk0yPY= X-Received: from pfbhu13.prod.google.com ([2002:a05:6a00:698d:b0:732:51fc:618f]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:2d04:b0:1f5:7b6f:f8e8 with SMTP id adf61e73a8af0-20113c095fdmr14665309637.6.1744044231220; Mon, 07 Apr 2025 09:43:51 -0700 (PDT) Date: Mon, 7 Apr 2025 09:43:50 -0700 In-Reply-To: <20250407161540.GG1557073@nvidia.com> Mime-Version: 1.0 References: <86y0wrlrxt.wl-maz@kernel.org> <86wmcbllg2.wl-maz@kernel.org> <20250331145643.GF10839@nvidia.com> <20250407161540.GG1557073@nvidia.com> Message-ID: Subject: Re: [PATCH v3 1/1] KVM: arm64: Allow cacheable stage 2 mapping using VMA flags From: Sean Christopherson To: Jason Gunthorpe Cc: Marc Zyngier , Ankit Agrawal , Catalin Marinas , Oliver Upton , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "will@kernel.org" , "ryan.roberts@arm.com" , "shahuang@redhat.com" , "lpieralisi@kernel.org" , "david@redhat.com" , Aniket Agashe , Neo Jia , Kirti Wankhede , "Tarun Gupta (SW-GPU)" , Vikram Sethi , Andy Currid , Alistair Popple , John Hubbard , Dan Williams , Zhi Wang , Matt Ochs , Uday Dhoke , Dheeraj Nigam , Krishnakant Jaju , "alex.williamson@redhat.com" , "sebastianene@google.com" , "coltonlewis@google.com" , "kevin.tian@intel.com" , "yi.l.liu@intel.com" , "ardb@kernel.org" , "akpm@linux-foundation.org" , "gshan@redhat.com" , "linux-mm@kvack.org" , "ddutile@redhat.com" , "tabba@google.com" , "qperret@google.com" , "kvmarm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 6DB6B40014 X-Stat-Signature: wzs53p66ui5q5k57ktfdq18uqpqfep73 X-HE-Tag: 1744044232-262416 X-HE-Meta: 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 eQM5nUJC 9+kXcDrj9QYTAUvW/erCsft8ZBshldhnxf0GLT3yWXq6VDafhpTRji3vHSbmHhGqzifNdG0gvif57um+J3wukefTPnWzKPbGp4lk9tGOYKVqXUgXrAd9ahHeSTZaPRFwP249XVP9SlXYcvodzC8T/reSUyRgEz1sw3ou/UwQyq+SD8zP/QrOHC6fadmM6wEX4JobnZCCSOArdXPMTWX+XlGeSTQVXFxteH0Oc8FdcshQKG2dcKvyjWw7sKBJP6ZrEAd3VNb5fSAfQwfP8hHBkEOz+lgxhnH9rxzwByNVy7I9W4mvqG6ZkA/3vYpk0ZfQ3DD2xsPYWCuY0HnQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000075, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Apr 07, 2025, Jason Gunthorpe wrote: > On Mon, Apr 07, 2025 at 08:20:09AM -0700, Sean Christopherson wrote: > > On Mon, Mar 31, 2025, Jason Gunthorpe wrote: > > > On Wed, Mar 26, 2025 at 11:24:32AM -0700, Sean Christopherson wrote: > > > > > I don't know how you reconcile the lack of host mapping and cache > > > > > maintenance. The latter cannot take place without the former. > > > > > > > > I assume cache maintenance only requires _a_ mapping to the physical memory. > > > > With guest_memfd, KVM has the pfn (which happens to always be struct page memory > > > > today), and so can establish a VA=>PA mapping as needed. > > > > > > This is why we are forcing FWB in this work, because we don't have a > > > VA mapping and KVM doesn't have the code to create one on demand. > > > > I don't follow. As it exists today, guest_memfd doesn't touch the direct map, > > i.e. there's already a kernel mapping, KVM doesn't need to create one. > > This is not about guest_memfd.. Heh, my part of the thread was. I was responding to Marc's comment: : Remind me how this work with stuff such as guestmemfd, which, by : definition, doesn't have a userspace mapping? I'm pretty sure we're on the same page.