From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DFB0DC433F5 for ; Mon, 20 Dec 2021 17:37:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Subject:Cc:To:From:Message-ID:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=tDm1dAPscMGSHXdz+biG6PQkA+2ZaVjLExG5YsvvA60=; b=y6p59iEyDqwzle l4kJuFpR8FYdtv+U1cOH9VzjmqhgbxY0a3hEfwMppbBAM7eiVnS17kyXYF0wRd0BQhY7AZZNdkxdb pkz8HRThf+3VBISN43Ny6u7iP05fRfUidqweSZrJ1n7YeWXn6/4/4gEjcl0PUrFcCfMAhH/sHWisi qUaerRAFF98tVd/IX/+lZGWDlzovyNyqUmvuLm/Aqa2y3UJNT2pIx5C+fElcRlqWR/MH+dgZliBKm RHjlNpJwMIYWnYtvavMlONqOQ6JsClRr70XNss/3o89R7r/111ghRF4i4usi90ToItSD4ENpZxXdJ vslNbjRylrlHms2qbQWA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mzMaF-003apJ-A7; Mon, 20 Dec 2021 17:36:23 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mzMaB-003aop-SP for linux-arm-kernel@lists.infradead.org; Mon, 20 Dec 2021 17:36:21 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 52B4161274; Mon, 20 Dec 2021 17:36:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B6057C36AE7; Mon, 20 Dec 2021 17:36:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1640021778; bh=hSkNL48LM2lfIkVYn4iz25mA/SDAA2AqhRSD7HSARqw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Pxchfln5VZRx5hpEFYFE35UPYdLGeczSLpzEd/QgjlbaxHVGp53buYk6M9FEfSEnm MqszzLzUtWTFddfS0p1P3Nxlq/72aTa1729VPCslhWcXN1FQ8ap+wW1vTIqULPoBIM Tr9uOvTQ3aTL+TUb8r8lFr0aFeS2DdLUNNaDKv9FiB01C0UFfGlSj6F2FL+r1LqG0I uswHjqcC7Hcfjho6k24JkJ8bSQV/Wi+12W9n8gaXtUQg6eLFnyDWuxR/mla1/WDV1H CowuJicN+eLdXCxXSEw4GKJGr/XzF7SgOeysHRSDn8JhyVYPABCnoyuH/XbwfoR/Lr Jn79fsanB0/lw== Received: from cfbb000407.r.cam.camfibre.uk ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mzMa8-00DMRs-Qv; Mon, 20 Dec 2021 17:36:16 +0000 Date: Mon, 20 Dec 2021 17:36:16 +0000 Message-ID: <8735mnw54f.wl-maz@kernel.org> From: Marc Zyngier To: D Scott Phillips Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Darren Hart , patches@amperecomputing.com Subject: Re: [PATCH v4] arm64: errata: Fix exec handling in erratum 1418040 workaround In-Reply-To: <8635mngrg2.fsf@scott-ph-mail.amperecomputing.com> References: <20211217211920.2004032-1-scott@os.amperecomputing.com> <87ee67wkj4.wl-maz@kernel.org> <8635mngrg2.fsf@scott-ph-mail.amperecomputing.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: scott@os.amperecomputing.com, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, darren@os.amperecomputing.com, patches@amperecomputing.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-20211220_093620_054262_5A7FDD3D X-CRM114-Status: GOOD ( 46.20 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 20 Dec 2021 16:40:45 +0000, D Scott Phillips wrote: > > Marc Zyngier writes: > > > On Fri, 17 Dec 2021 21:19:20 +0000, > > D Scott Phillips wrote: > >> > >> The erratum 1418040 workaround enables vct access trapping when executing > > > > nit: s/vct/CNTVCT_EL1/. > > fixed, thanks > > >> compat threads. The workaround is applied when switching between tasks, but > >> the need for the workaround could also change at an exec(), when a > >> non-compat task execs a compat binary or vice versa. Apply the workaround > >> in arch_setup_new_exec(). > >> > >> The leaves a small window of time between SET_PERSONALITY and > >> arch_setup_new_exec where preemption could occur and confuse the old > >> workaround logic that compares TIF_32BIT between prev and next. Instead, we > >> can just read cntkctl to make sure it's in the state that the next task > >> needs. I measured cntkctl read time to be about the same as a mov from a > >> general-purpose register on N1. Update the workaround logic to examine the > >> current value of cntkctl instead of the previous task's compat state. > >> > >> Fixes: d49f7d7376d0 ("arm64: Move handling of erratum 1418040 into C code") > >> Signed-off-by: D Scott Phillips > >> Cc: # 5.4.x > >> --- > >> > >> v4: - Move exec() handling into arch_setup_new_exec(), drop prev32==next32 > >> comparison to fix possible confusion in the small window between > >> SET_PERSONALITY() and arch_setup_new_exec(). (Catalin) > >> > >> v3: - Un-nest conditionals (Marc) > >> > >> v2: - Use sysreg_clear_set instead of open coding (Marc) > >> - guard this_cpu_has_cap() check under IS_ENABLED() to avoid tons of > >> WARN_ON(preemptible()) when built with !CONFIG_ARM64_ERRATUM_1418040 > >> > >> arch/arm64/kernel/process.c | 34 ++++++++++++---------------------- > >> 1 file changed, 12 insertions(+), 22 deletions(-) > >> > >> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > >> index aacf2f5559a8..b37ff23e625e 100644 > >> --- a/arch/arm64/kernel/process.c > >> +++ b/arch/arm64/kernel/process.c > >> @@ -439,34 +439,23 @@ static void entry_task_switch(struct task_struct *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 > >> + * Ensure access is disabled when switching to a 32bit task, ensure > >> + * access is enabled when switching to a 64bit task. > >> */ > >> -static void erratum_1418040_thread_switch(struct task_struct *prev, > >> - struct task_struct *next) > >> +static void erratum_1418040_thread_switch(struct task_struct *next) > >> { > >> - bool prev32, next32; > >> - u64 val; > >> - > >> - if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040)) > >> - return; > >> + preempt_disable(); > > > > I'd rather avoid this on the __switch_to() path. We're guaranteed to > > be non-preemptible when called from there, and we want it to be as > > fast as possible. It would also avoid the bug on the early return just > > below. > > Yes, makes sense. I've added an erratum_1418040_new_exec() helper that > does preempt_disable/erratum_14518040_thread_switch(current)/preempt_enable, > and called it from arch_setup_new_exec(). Yes, that's much better. > > >> > >> - prev32 = is_compat_thread(task_thread_info(prev)); > >> - next32 = is_compat_thread(task_thread_info(next)); > >> - > >> - if (prev32 == next32 || !this_cpu_has_cap(ARM64_WORKAROUND_1418040)) > >> + if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040) || > >> + !this_cpu_has_cap(ARM64_WORKAROUND_1418040)) > >> return; > >> > >> - val = read_sysreg(cntkctl_el1); > >> - > >> - if (!next32) > >> - val |= ARCH_TIMER_USR_VCT_ACCESS_EN; > >> + if (is_compat_thread(task_thread_info(next))) > >> + sysreg_clear_set(cntkctl_el1, ARCH_TIMER_USR_VCT_ACCESS_EN, 0); > >> else > >> - val &= ~ARCH_TIMER_USR_VCT_ACCESS_EN; > >> + sysreg_clear_set(cntkctl_el1, 0, ARCH_TIMER_USR_VCT_ACCESS_EN); > >> > >> - write_sysreg(val, cntkctl_el1); > >> + preempt_enable(); > >> } > >> > >> /* > >> @@ -501,7 +490,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev, > >> contextidr_thread_switch(next); > >> entry_task_switch(next); > >> ssbs_thread_switch(next); > >> - erratum_1418040_thread_switch(prev, next); > >> + erratum_1418040_thread_switch(next); > >> ptrauth_thread_switch_user(next); > >> > >> /* > >> @@ -611,6 +600,7 @@ void arch_setup_new_exec(void) > >> current->mm->context.flags = mmflags; > >> ptrauth_thread_init_user(); > >> mte_thread_init_user(); > >> + erratum_1418040_thread_switch(current); > > > > But what is the point of this now? As you enter __switch_to(), the TIF > > flags are set in stone for this particular return to userspace. > > > > Since you are now evaluating the state of CNTKCTL_EL1 on each and > > every switch, you are guaranteed to set the enable bit to the right > > value on each return to userspace, even if you have gone via > > SET_PERSONALITY(). > > > > Am I missing something? > > The workaround in __switch_to isn't happening for every return to > userspace, but rather for every scheduler task switch. When a process > exec()s, no switch happens at that point. From the scheduler point of > view, this is still the same task. So in the time period between > exec()ing a compat task from non-compat (or vice versa) and the first > time it gets switched out, we would apply the wrong workaround state, > unless we make a change to cntkctl from exec() before returning back to > EL0. Right. For $reason, I keep equating task switch and return to user. Thanks for spelling it out for me. M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel