Hi Catalin,
On 1/11/2021 10:41 AM, Catalin Marinas wrote:
Hi Marc,
On Mon, Jan 11, 2021 at 01:27:59PM +0000, Marc Zyngier wrote:
Add a facility to globally override a feature, no matter what
the HW says. Yes, this is dangerous.
Yeah, it's dangerous. We can make it less so if we only allow safe
values (e.g. lower if FTR_UNSIGNED).
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9a555809b89c..465d2cb63bfc 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -75,6 +75,8 @@ struct arm64_ftr_reg {
u64 sys_val;
u64 user_val;
const struct arm64_ftr_bits *ftr_bits;
+ u64 *override_val;
+ u64 *override_mask;
};
At the arm64_ftr_reg level, we don't have any information about the safe
values for a feature. Could we instead move this to arm64_ftr_bits? We
probably only need a single field. When populating the feature values,
we can make sure it doesn't go above the hardware one.
I attempted a feature modification for MTE here, though I dropped the
entire series in the meantime as we clarified the ARM ARM:
https://lore.kernel.org/linux-arm-kernel/20200515171612.1020-24-catalin.marinas@xxxxxxx/
Srinivas copied it in his patch (but forgot to give credit ;)):
Sorry about that. I did mention that its taken from your patch-set in my
cover letter. But missed your signed-off-by in the patch.
https://lore.kernel.org/linux-arm-msm/6dfdf691b5ed57df81c4c61422949af5@xxxxxxxxxxxxxxx/T/#m1ae76e6096c07ab5f1636a4e383a3fd6cfb4665f
Since we can ignore my patch with the mechanism added by Marc, I am not
re-sending this. Thanks.
https://lore.kernel.org/linux-arm-msm/1610152163-16554-3-git-send-email-sramana@xxxxxxxxxxxxxx/
The above adds a filter function but, instead, just use your mechanism in
this series for idreg.feature setting via cmdline. The arm64_ftr_value()
function extracts the hardware value and lowers it if a cmdline argument
was passed.
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