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AJvYcCXaScJDnHLsidtJL0RpkIq0B/ZivEHKNy8yppodygtoVro0kRAKKbiLHXP9AaDU2PjKmIqZ9BRvvA==@kvack.org X-Gm-Message-State: AOJu0Yy4UscK0K/Ge1yvYj82wTAPuy15+xxHFn9vZpRXTxkHo1yve8pT VqXRKhjFQQtKvAJTh94dgeJXUWHtRGA4/B+gVRIiH4ME7Qn2VQtoYG0VOdSzvoxvjGB8Q7bBMAv PqQ== X-Google-Smtp-Source: AGHT+IHFT5IWpb0wEWYBsgf38l3iAGlVDr2qHVuyYE70TQA84d8Gl7Htq0vtNTpBGTTuOvXXCqA42VAV2Ds= X-Received: from pfbhg1.prod.google.com ([2002:a05:6a00:8601:b0:736:3d80:706e]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:3bc8:b0:223:5124:a16e with SMTP id d9443c01a7336-22a8a048ffamr208407455ad.5.1744039210859; Mon, 07 Apr 2025 08:20:10 -0700 (PDT) Date: Mon, 7 Apr 2025 08:20:09 -0700 In-Reply-To: <20250331145643.GF10839@nvidia.com> Mime-Version: 1.0 References: <20250319192246.GQ9311@nvidia.com> <86y0wrlrxt.wl-maz@kernel.org> <86wmcbllg2.wl-maz@kernel.org> <20250331145643.GF10839@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-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 1C5111C000A X-Stat-Signature: e75swxcma1mdifwszi9t1xzpj7h5zkki X-Rspam-User: X-HE-Tag: 1744039211-415549 X-HE-Meta: U2FsdGVkX19BCF5i0Bb87EMGQ0fRMdiXiAldmMCTZebUt8KGGHFDMnqZa1Muiw+2bS7QwErmttt0VswNX9vFESnvaMGgXGXzL/KuZF6gD83Y6btQPLAjIIDgJWiYdt2AXVIX3hHrk9OfgsWvKoUFcV5Nlr3DldUQWws4QMs0KZIpY8AaUQPmVruwYskBJ3DQzTFfk17eQXVRVhrHTLsS/bSYWwgJb8bVwKvUFIr4BclpvE6sXXx3izAb93HqfUortk7+zY3VGkyfj0TAqc9+dllCdZtErUw9GQpuuVuzvBsRpZKB8/SX8VlPyX6jYgfsiF5GfHyWeoK7XcOvFDzXSOS7RH0Dq6sECbLwRK3/W728C4Q0Hf56Uxs/20rgSD3Am7tszyeE/6XWm26sOYPj7S+WRudavSZXkefamB7PNiIL4KPlNFfGz6XANVogdxZyRmTmFrtbsoxO2afhTexQ695yOvbq6IgHjf4MmKt13Cmgrfgx0kCYPpeYhdKHqcDUlV4d923tvExTG5Av2Q3FkcK2WzK0l3Eh472hKw6AkuG09iCDb8E1BeahX8CeWTgpSZs5jUGA3lKlQVI0Dy3wWM7o7Z+Tm7X5NNFKy4LK3Bu2A9w5SeXhBoDHIs5vYb8OpLKYXxm0XdrdBbmQrodprfLv5kIc+gaPelNkM16bTUNfmONVGJNZzz4NsUyXyYx//ISBo7RV8XCAl9l9kP0MqpLV4Ow3a4/4Yc0PIagrjzkeq4vSJU26rIG3Pe5lHbR2uDm6VuYVOB7c7fTkONEH74SazkJr96U4CeDFaujSrRgV+Z0nSAa1KZmVn17tS5DWbySEkam2x0JJFyD5PNMJqVCVlKLWLipmmd4D7UJ2NKGuTTBieHHN0Xlxxic19JbNHKEEm43pCpyT5xP9Zk5/iVhM6esVDGt7Ff960aL8HzhVL4MW1evLBioHRTdqsSxrO4d2qR8AjwhmnTVv4jL LUBypQM+ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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, 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.