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Date: Thu, 18 May 2017 13:39:12 +0100 From: Suzuki K Poulose <Suzuki.Poulose@....com> To: Leo Yan <leo.yan@...aro.org> Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Mark Rutland <mark.rutland@....com>, Marc Zyngier <marc.zyngier@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, James Morse <james.morse@....com>, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Guodong Xu <guodong.xu@...aro.org>, Haojian Zhuang <haojian.zhuang@...aro.org>, Douglas Raillard <douglas.raillard@....com> Subject: Re: [PATCH] arm64: cpufeature: check translation granule size based on kernel config On 18/05/17 12:36, Leo Yan wrote: > Hi Suzuki, > > 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 Which production branch do you mean above ? Is it something in your intenral repository ? Suzuki
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