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([2601:646:c200:1ef2:d2f:b9d:749:9ce5]) by smtp.gmail.com with ESMTPSA id g65sm14766552pfb.61.2020.06.15.14.18.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Jun 2020 14:18:42 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID Date: Mon, 15 Jun 2020 14:18:39 -0700 Message-Id: References: <3908561D78D1C84285E8C5FCA982C28F7F66C849@ORSMSX115.amr.corp.intel.com> Cc: "Yu, Fenghua" , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , David Woodhouse , Lu Baolu , Frederic Barrat , Andrew Donnellan , Felix Kuehling , Joerg Roedel , "Hansen, Dave" , "Raj, Ashok" , "Pan, Jacob jun" , "Jiang, Dave" , "Yu, Yu-cheng" , "Mehta, Sohil" , "Shankar, Ravi V" , linux-kernel , x86 , "iommu@lists.linux-foundation.org" , amd-gfx , linuxppc-dev In-Reply-To: <3908561D78D1C84285E8C5FCA982C28F7F66C849@ORSMSX115.amr.corp.intel.com> To: "Luck, Tony" X-Mailer: iPhone Mail (17F80) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jun 15, 2020, at 1:56 PM, Luck, Tony wrote: >=20 > =EF=BB=BF >>=20 >> Are we planning to keep PASID live once a task has used it once or are we= going to swap it lazily? If the latter, a percpu variable might be better.= >=20 > Current plan is "touch it once and the task owns it until exit(2)" >=20 > Maybe someday in the future when we have data on how applications > actually use accelerators we could look at something more complex > if usage patterns look like it would be beneficial. >=20 >=20 So what=E2=80=99s the RDMSR for? Surely you have some state somewhere that says =E2=80=9Cthis task has a PASID.=E2=80=9D= Can=E2=80=99t you just make sure that stays in sync with the MSR? Then, o= n #GP, if the task already has a PASID, you know the MSR is set.=