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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qCWpIZJyle1CnxF0mfzL51ZZrc+lgi1FCWufg+fdD4C3LnAhAdqG+yOAQVUktlhQj p1q2ujxe01GN/YlR+g5ypXIuoNQei3uuNybBMEsgxyF8q7twxpCp0dzAIf+vlZyrM1 xQJ0F5GV8r0lEw0yR9/mBskoHU06Y0xqJ3sjjJpQ= Date: Thu, 3 Sep 2026 11:28:08 +0530 From: Linu Cherian To: Kevin Brodsky Cc: linux-hardening@vger.kernel.org, Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , "David Hildenbrand (Arm)" , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , =?iso-8859-1?Q?Pierre-Cl=E9ment?= Tosi , Quentin Perret , Rick Edgecombe , Ryan Roberts , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org, Ira Weiny , Lorenzo Stoakes , Thomas Gleixner Subject: Re: [PATCH RFC v9 07/25] arm64: Context-switch POR_EL1 Message-ID: References: <20260818-kpkeys-v9-0-743ad31b2c8f@arm.com> <20260818-kpkeys-v9-7-743ad31b2c8f@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260818-kpkeys-v9-7-743ad31b2c8f@arm.com> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2F7D11C0003 X-Stat-Signature: f86m3exyajgk9q9g7wieoie4xegnbgxn X-HE-Tag: 1788415093-294926 X-HE-Meta: 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 SEMNrMIh +LntJvVE3k9YD57E2wrITyl7PyJ6rLimScN9tuSCIwZ4i8GxXDrewQUW3BbjTqLCBfM0eK4Sk1/CaIusdBGODdDIYWlksXdFYAOPSpFcOedYbMH+44d/cCfJwljJsIyo2OZz1e+VVV+6zZ1/NefRx3/0L2Zq4J9tTwiciApm1hRzcEc4ygVH6l5l8ERHvQbh7/hN2d3lAzvdTeAokDjU6vU/fXXconhg0XEm35dI+lmxVTk9ukMiW+kma7eZGpJavGFCFRpKOGtmaTt4cPBCGnbQrX6ki78ffAyNbJIOk3c3UZGOzss7a5mSWSR8I82tjFc/UT177MKl+veySraopn56e9GkSai4+MF6w9vGk0J9kKm5H/BVl1YdiwEsa0UTod7tVKMoA4BxHXPtmw0oGGibqzRKPbnNmYMA1NpbD1lPDBs8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 18, 2026 at 03:08:49PM +0100, Kevin Brodsky wrote: > POR_EL1 is about to be used by the kpkeys framework, modifying it > for (typically small) sections of code. If an exception occurs > during that window and scheduling occurs, we must ensure that > POR_EL1 is context-switched as needed (saving the old value and > restoring the new one). An ISB is needed to ensure the write takes > effect, so we skip it if the new value is the same as the old, like > for POR_EL0. > > Signed-off-by: Kevin Brodsky > --- > arch/arm64/include/asm/processor.h | 1 + > arch/arm64/kernel/process.c | 10 ++++++++++ > 2 files changed, 11 insertions(+) > > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index c2a627f39314..8d7fa479cd36 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -195,6 +195,7 @@ struct thread_struct { > u64 svcr; > u64 tpidr2_el0; > u64 por_el0; > + u64 por_el1; > #ifdef CONFIG_ARM64_GCS > unsigned int gcs_el0_mode; > unsigned int gcs_el0_locked; > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index 581f80e9b9b7..1dec143decf1 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -51,6 +51,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -431,6 +432,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) > > ptrauth_thread_init_kernel(p); > > + if (system_supports_poe()) > + p->thread.por_el1 = POR_EL1_INIT; > + > if (likely(!args->fn)) { > *childregs = *current_pt_regs(); > childregs->regs[0] = 0; > @@ -681,6 +685,12 @@ static void permission_overlay_switch(struct task_struct *next) > * of POR_EL0. > */ > } > + > + current->thread.por_el1 = read_sysreg_s(SYS_POR_EL1); > + if (current->thread.por_el1 != next->thread.por_el1) { > + write_sysreg_s(next->thread.por_el1, SYS_POR_EL1); > + isb(); > + } > } > > /* Reviewed-by: Linu Cherian