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[2003:cb:c705:ab00:f9b6:da12:cad4:6642]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36394d5ef0dsm1579567f8f.64.2024.06.19.05.17.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Jun 2024 05:17:24 -0700 (PDT) Message-ID: <095dd4fb-956b-40f4-984d-14544d726f97@redhat.com> Date: Wed, 19 Jun 2024 14:17:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 0/5] mm/gup: Introduce exclusive GUP pinning To: Jason Gunthorpe , Fuad Tabba Cc: John Hubbard , Elliot Berman , Andrew Morton , Shuah Khan , Matthew Wilcox , maz@kernel.org, kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, pbonzini@redhat.com References: <20240618-exclusive-gup-v1-0-30472a19c5d1@quicinc.com> <7fb8cc2c-916a-43e1-9edf-23ed35e42f51@nvidia.com> <14bd145a-039f-4fb9-8598-384d6a051737@redhat.com> <20240619115135.GE2494510@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: q55t4ecrxb6uj5g49o7g5ofribdxyana X-Rspamd-Queue-Id: 0E489180010 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1718799448-312290 X-HE-Meta: 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 slZfQ9Xu 3Aro2MyAKnLdw2ouWRwayBu6KizORU9Xu2oSGJFuGektoqYamCqwb9cZHyhdTNRyjmd4cgPQqiHCNC0koDwqtNPX/9ZTQJT/QIBloFS+dDmW0lXiuyQ0mA+O9D/s+9Vt7P3I2LfWjmusQefFfgL2jlUZwM08u3MsmDaZb2uNEtCWBGGF7g0J8WuROJ90HzEJSqOaLQB9qcF/LyscoJiiSGzy3lvmcMOZoyrjaBSfECnlMabkp8Sd9FalOh+Rl5Pj6B52dYRbEpQKuMDbyC4fXnTSLX53XYz98Qya/vAQuVcbZf1UIMCPmjALOdVrjsToro3kiWLhfBtAyRdw29mL23JUs2H1nNy/Meyhb0l4ZHDHqx0LrdookQzWw4A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > If the memory can't be accessed by the CPU then it shouldn't be mapped > into a PTE in the first place. The fact you made userspace faults > (only) work is nifty but still an ugly hack to get around the fact you > shouldn't be mapping in the first place. > > We already have ZONE_DEVICE/DEVICE_PRIVATE to handle exactly this > scenario. "memory" that cannot be touched by the CPU but can still be > specially accessed by enlightened components. > > guest_memfd, and more broadly memfd based instead of VMA based, memory > mapping in KVM is a similar outcome to DEVICE_PRIVATE. > > I think you need to stay in the world of not mapping the memory, one > way or another. Fully agreed. Private memory shall not be mapped. -- Cheers, David / dhildenb