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[2003:d8:2f2c:5500:988:23f9:faa0:7232]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454a9bcef22sm57156535e9.19.2025.07.04.07.15.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Jul 2025 07:15:30 -0700 (PDT) Message-ID: <29cc7d2a-b174-4ed3-ae1a-22db478c62ec@redhat.com> Date: Fri, 4 Jul 2025 16:15:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 6/6] KVM: arm64: Expose new KVM cap for cacheable PFNMAP To: Jason Gunthorpe , ankita@nvidia.com Cc: maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, ryan.roberts@arm.com, shahuang@redhat.com, lpieralisi@kernel.org, ddutile@redhat.com, seanjc@google.com, aniketa@nvidia.com, cjia@nvidia.com, kwankhede@nvidia.com, kjaju@nvidia.com, targupta@nvidia.com, vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com, jhubbard@nvidia.com, danw@nvidia.com, zhiw@nvidia.com, mochs@nvidia.com, udhoke@nvidia.com, dnigam@nvidia.com, 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, tabba@google.com, qperret@google.com, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, maobibo@loongson.cn References: <20250621042111.3992-1-ankita@nvidia.com> <20250621042111.3992-7-ankita@nvidia.com> <20250704134413.GE1410929@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250704_071535_706436_BE448E77 X-CRM114-Status: GOOD ( 17.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 04.07.25 15:44, Jason Gunthorpe wrote: > On Sat, Jun 21, 2025 at 04:21:11AM +0000, ankita@nvidia.com wrote: >> From: Ankit Agrawal >> >> Introduce a new KVM capability to expose to the userspace whether >> cacheable mapping of PFNMAP is supported. >> >> The ability to safely do the cacheable mapping of PFNMAP is contingent >> on S2FWB and ARM64_HAS_CACHE_DIC. S2FWB allows KVM to avoid flushing >> the D cache, ARM64_HAS_CACHE_DIC allows KVM to avoid flushing the icache >> and turns icache_inval_pou() into a NOP. The cap would be false if >> those requirements are missing and is checked by making use of >> kvm_arch_supports_cacheable_pfnmap. >> >> This capability would allow userspace to discover the support. >> It could for instance be used by userspace to prevent live-migration >> across FWB and non-FWB hosts. >> >> CC: Catalin Marinas >> CC: Jason Gunthorpe >> CC: Oliver Upton >> CC: David Hildenbrand >> Suggested-by: Marc Zyngier >> Signed-off-by: Ankit Agrawal >> --- >> Documentation/virt/kvm/api.rst | 13 ++++++++++++- >> arch/arm64/kvm/arm.c | 7 +++++++ >> include/uapi/linux/kvm.h | 1 + >> 3 files changed, 20 insertions(+), 1 deletion(-) > > I don't know if any VMM will ever use this, but it looks OK So, should we defer it to the point where we actually have a use case? I mean, patch #4 could be simplified by modifying arm64 code in patch #5 only. No need for a common kvm_arch function etc. -- Cheers, David / dhildenb