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([2600:1010:b01f:cba8:c05f:3a2c:209d:43f4]) by smtp.gmail.com with ESMTPSA id r23-v6sm26036585pfh.79.2018.10.19.09.59.01 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Oct 2018 09:59:02 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (1.0) Subject: Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads From: Andy Lutomirski X-Mailer: iPhone Mail (16A366) In-Reply-To: <2fe82232-4e80-8317-757c-d2235c4633d8@redhat.com> Date: Fri, 19 Oct 2018 09:59:00 -0700 Cc: Sebastian Andrzej Siewior , Andrew Lutomirski , Dave Hansen , LKML , X86 ML , Radim Krcmar , kvm list , "Jason A. Donenfeld" , Rik van Riel Content-Transfer-Encoding: quoted-printable Message-Id: <9BAD5065-AA1B-4DEF-A9D4-D7FD9B46667E@amacapital.net> References: <20181004140547.13014-1-bigeasy@linutronix.de> <20181004140547.13014-6-bigeasy@linutronix.de> <39e0a55f-4920-cfde-9bef-09c51109d211@linux.intel.com> <20181018162644.qqjkzoqn2fleyi2b@linutronix.de> <20181018182538.vgotfpsdy7qxl2tg@linutronix.de> <2fe82232-4e80-8317-757c-d2235c4633d8@redhat.com> To: Paolo Bonzini Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Oct 19, 2018, at 12:44 AM, Paolo Bonzini wrote: >=20 > On 18/10/2018 22:46, Andy Lutomirski wrote: >>> [0] drivers/usb/gadget/function/f_fs.c::ffs_user_copy_worker() >>>=20 >>> Sebastian >> I think we need an entirely new API: >>=20 >> user_mm_ctx_t ctx =3D user_mm_ctx_get(); >>=20 >> ... >>=20 >> use_user_mm_ctx(ctx); >> unuse_user_mm_ctx(ctx); >>=20 >> ... >>=20 >> user_mm_ctx_put(ctx); >>=20 >> and ctx will store a copy of mm and PKRU. >>=20 >=20 > That looks like a good API in general. The ffs_user_copy_worker that > Sebastian mentioned seems to be used by AIO, in which case of course it > has to happen in a kernel thread. >=20 > But while the API is good, deciding on the desired semantics is > "interesting". The submitting thread might be changing PKRU between the > time the I/O operation is submitted and the time it is completed, for > example. I think there=E2=80=99s only one sensible answer: capture PKRU at the time o= f submission.=