Re: [PATCH] arm64: cpufeature: check translation granule size based on kernel config
From: Suzuki K Poulose
Date: Thu May 18 2017 - 08:39:24 EST
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