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Fri, 31 Jul 2020 12:14:41 +0100 MIME-Version: 1.0 Date: Fri, 31 Jul 2020 12:14:40 +0100 From: Marc Zyngier To: Will Deacon Subject: Re: [PATCH v2 1/2] arm64: Move handling of erratum 1418040 into C code In-Reply-To: <20200731104121.GA26500@willie-the-truck> References: <20200731083358.50058-1-maz@kernel.org> <20200731083358.50058-2-maz@kernel.org> <20200731104121.GA26500@willie-the-truck> User-Agent: Roundcube Webmail/1.4.5 Message-ID: <98dc0a0f6511542eae26b91d925f160e@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: will@kernel.org, linux-arm-kernel@lists.infradead.org, saiprakash.ranjan@codeaurora.org, catalin.marinas@arm.com, suzuki.poulose@arm.com, swboyd@chromium.org, dianders@google.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200731_071444_352003_81529843 X-CRM114-Status: GOOD ( 23.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sai Prakash Ranjan , Suzuki K Poulose , Catalin Marinas , Stephen Boyd , dianders@google.com, kernel-team@android.com, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-07-31 11:41, Will Deacon wrote: > On Fri, Jul 31, 2020 at 09:33:57AM +0100, Marc Zyngier wrote: >> Instead of dealing with erratum 1418040 on each entry and exit, >> let's move the handling to __switch_to() instead, which has >> several advantages: >> >> - It can be applied when it matters (switching between 32 and 64 >> bit tasks). >> - It is written in C (yay!) >> - It can rely on static keys rather than alternatives >> >> Tested-by: Sai Prakash Ranjan >> Signed-off-by: Marc Zyngier >> --- >> arch/arm64/kernel/entry.S | 21 --------------------- >> arch/arm64/kernel/process.c | 35 +++++++++++++++++++++++++++++++++++ >> 2 files changed, 35 insertions(+), 21 deletions(-) > > [...] > >> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c >> index 6089638c7d43..8bbf066224ab 100644 >> --- a/arch/arm64/kernel/process.c >> +++ b/arch/arm64/kernel/process.c >> @@ -515,6 +515,40 @@ static void entry_task_switch(struct task_struct >> *next) >> __this_cpu_write(__entry_task, next); >> } >> >> +/* >> + * ARM erratum 1418040 handling, affecting the 32bit view of CNTVCT. >> + * Assuming the virtual counter is enabled at the beginning of times: >> + * >> + * - disable access when switching from a 64bit task to a 32bit task >> + * - enable access when switching from a 32bit task to a 64bit task >> + */ >> +static __always_inline > > Do we need the __always_inline? None of the other calls from > __switch_to() > have it. Suggestion from Stephen. In my experience, it doesn't change much as most things get inlined anyway. Happy to drop it. > >> +void erratum_1418040_thread_switch(struct task_struct *prev, >> + struct task_struct *next) >> +{ >> + bool prev32, next32; >> + u64 val; >> + >> + if (!(IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040) && >> + cpus_have_const_cap(ARM64_WORKAROUND_1418040))) >> + return; >> + >> + prev32 = is_compat_thread(task_thread_info(prev)); >> + next32 = is_compat_thread(task_thread_info(next)); >> + >> + if (prev32 == next32) >> + return; >> + >> + val = read_sysreg(cntkctl_el1); >> + >> + if (prev32 & !next32) > > I know they're bools but this is perverse! Well, this is me writing this code, so don't attribute to perversity what can adequately be explained by a silly typo... ;-) > Why can't it just be: > > if (next32) > val &= ~ARCH_TIMER_USR_VCT_ACCESS_EN; > else > val |= ARCH_TIMER_USR_VCT_ACCESS_EN; > > ? Yup, that's better. Do you want to apply these changes directly, or should I repin it? M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel