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charset=us-ascii Content-Disposition: inline In-Reply-To: <20240823170835.GA1181@willie-the-truck> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1281FA000B X-Stat-Signature: 8s1a5qsbbwfnww3qw59xrf3na67641ks X-Rspam-User: X-HE-Tag: 1724438460-744086 X-HE-Meta: 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 KVmxSmDs dypy79gF4nt/Q2rZaXxKZpADmab1EIU18yqRf1rlqDJNg7+Hq2H1IKWv7klWes2KbUA5Q1ZRXk1rGga3pFj90d6qAumVP7EbXiMD2VG5TFTqtnfW6nVLNP9v9SOpBx6tYK2DH76nwCGjoVXvsjmobGifvatC1xMyDSntVfE8kTIYnmK0T3/2eD3+IZOM869Nl3FlLj9xOA0ADiyT+U2qIWHpu8cV+9cOLH6YOMYad8w7z3afaPYgYYhe8P0ePfWezciH+yYbMbS7ZwMEOddXG3pBOWOPrxxBQrD/QE/ZSh0ddQas7hMP/D4fi6PG+eqLRU1YVCV6phjtgUjfgTUlcDLOCi0xzRC+HJxgBkhSqB/BH9f+SmcRNfxT1P6QPCtZASMpeynqSD9nXuIw= 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: On Fri, Aug 23, 2024 at 06:08:36PM +0100, Will Deacon wrote: > On Fri, Aug 23, 2024 at 05:41:06PM +0100, Catalin Marinas wrote: > > On Fri, Aug 23, 2024 at 03:45:32PM +0100, Will Deacon wrote: > > > On Thu, Aug 22, 2024 at 04:10:49PM +0100, Joey Gouly wrote: > > > > +static void permission_overlay_switch(struct task_struct *next) > > > > +{ > > > > + if (!system_supports_poe()) > > > > + return; > > > > + > > > > + current->thread.por_el0 = read_sysreg_s(SYS_POR_EL0); > > > > + if (current->thread.por_el0 != next->thread.por_el0) { > > > > + write_sysreg_s(next->thread.por_el0, SYS_POR_EL0); > > > > + /* ISB required for kernel uaccess routines when chaning POR_EL0 */ > > > > > > nit: typo "chaning". > > > > > > But more substantially, is this just to prevent spurious faults in the > > > context of a new thread using a stale value for POR_EL0? > > > > Not just prevent faults but enforce the permissions from the new > > thread's POR_EL0. The kernel may continue with a uaccess routine from > > here, we can't tell. > > Hmm, I wondered if that was the case. It's a bit weird though, because: > > - There's a window between switch_mm() and switch_to() where you might > reasonably expect to be able to execute uaccess routines I don't think we can have any uaccess between these two switches (a uaccess could fault, that's a pretty weird state between these two). > - kthread_use_mm() doesn't/can't look at this at all No, but a kthread would have it's own, most permissive, POR_EL0. > - GUP obviously doesn't care > > So what do we actually gain by having the uaccess routines honour this? I guess where it matters is more like not accidentally faulting because the previous thread had more restrictive permissions. -- Catalin