From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Thu, 18 May 2017 13:41:15 +0100 Subject: [PATCH] arm64: cpufeature: check translation granule size based on kernel config In-Reply-To: <20170518123840.GD21359@arm.com> References: <1495102873-10858-1-git-send-email-leo.yan@linaro.org> <20170518113627.GC25294@leoy-ThinkPad-T440> <20170518123840.GD21359@arm.com> Message-ID: <20170518124115.GC4957@leverpostej> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, May 18, 2017 at 01:38:41PM +0100, Will Deacon wrote: > On Thu, May 18, 2017 at 07:36:27PM +0800, Leo Yan wrote: > > On Thu, May 18, 2017 at 11:39:01AM +0100, Suzuki K Poulose wrote: > > > On 18/05/17 11:21, Leo Yan wrote: > > > >In the big.LITTLE system with two clusters, one is CA53 cluster and > > > >another is CA73 cluster. CA53 doesn't support 16KB memory translation > > > >granule size (4.3.21 AArch64 Memory Model Feature Register 0, EL1; ARM > > > >DDI 0500F), but CA73 supports this feature (4.3.27 AArch64 Memory Model > > > >Feature Register 0, EL1; ARM 100048_0002_04_en). As result, the kernel > > > >reports log for "Unexpected variation" as below. > > > > > > > >[ 0.182113] CPU features: SANITY CHECK: Unexpected variation in SYS_ID_AA64MMFR0_EL1. Boot CPU: 0x00000000001122, CPU4: 0x00000000101122 > > > > > > > > > > >This patch is to change the checking CPU feature for memory translation > > > >granule size based on kernel configuration. If kernel configuration has > > > >selected to use one specific memory translation granule size, then we > > > >will do strict sanity checking cross all CPUs. Otherwise we can skip to > > > >check unused features for memory translation granule size if kernel > > > >doesn't use it. > > > > > > > > > > If we were to suppress the warning (more on that below), we could simply > > > make this feature a NON_STRICT, since the unsupported CPUs won't boot > > > with 16K to hit this sanity check. > > > > > > However, there is a problem with disabling this warning. If a VM starts > > > using 16KB page size on a 4K/64K host, the VM could end up in unknown > > > failures when it switches to an unsupported CPU (after it has booted). > > > Of course the real fix lies in making the KVM exposing the safe value > > > for granule support to the VCPUs (which is currently being worked on by > > > Douglas in Cc). So, when we have that ready, we could make it NON_STRICT > > > instead of this approach. > > > > Thanks for the info :) > > > > I will use below patch for production branch temporarily. You could > > work out one formal patch for upstreaming when the dependency patches > > are get ready: > > The other thing we could do is change the way we taint on mismatch so that > we don't dump the scary (and pointless) backtrace. The backtrace is due to the WARN part of the WARN_TAINT_ONCE. We could chagne that as below, if we really want to get rid of the backtrace. Thanks, Mark. ---->8---- diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 94b8f7f..1f53314 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -639,8 +639,8 @@ void update_cpu_features(int cpu, * Mismatched CPU features are a recipe for disaster. Don't even * pretend to support them. */ - WARN_TAINT_ONCE(taint, TAINT_CPU_OUT_OF_SPEC, - "Unsupported CPU feature variation.\n"); + pr_warn_once("Unsupported CPU feature variation detected.\n"); + add_taint(TAINT_CPU_OUT_OF_SPEC); } u64 read_sanitised_ftr_reg(u32 id)