Messages in this thread | | | Date | Thu, 18 May 2017 13:38:41 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm64: cpufeature: check translation granule size based on kernel config |
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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.
Will
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