On 2021-01-12 11:50, Marc Zyngier wrote:
Hi Suzuki,
On 2021-01-12 09:17, Suzuki K Poulose wrote:
Hi Marc,
On 1/11/21 7:48 PM, Marc Zyngier wrote:
[...]
diff --git a/arch/arm64/kernel/cpufeature.c
b/arch/arm64/kernel/cpufeature.c
index 894af60b9669..00d99e593b65 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -774,6 +774,7 @@ static void __init init_cpu_ftr_reg(u32 sys_reg,
u64 new)
u64 strict_mask = ~0x0ULL;
u64 user_mask = 0;
u64 valid_mask = 0;
+ u64 override_val = 0, override_mask = 0;
const struct arm64_ftr_bits *ftrp;
struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg);
@@ -781,9 +782,35 @@ static void __init init_cpu_ftr_reg(u32 sys_reg,
u64 new)
if (!reg)
return;
+ if (reg->override_mask && reg->override_val) {
+ override_mask = *reg->override_mask;
+ override_val = *reg->override_val;
+ }
+
for (ftrp = reg->ftr_bits; ftrp->width; ftrp++) {
u64 ftr_mask = arm64_ftr_mask(ftrp);
s64 ftr_new = arm64_ftr_value(ftrp, new);
+ s64 ftr_ovr = arm64_ftr_value(ftrp, override_val);
+
+ if ((ftr_mask & override_mask) == ftr_mask) {
+ if (ftr_ovr < ftr_new) {
Here we assume that all the features are FTR_LOWER_SAFE. We could
probably use arm64_ftr_safe_value(ftrp, ftr_new, ftr_ovr) here ?
That would cover us for both HIGHER_SAFE and LOWER_SAFE features.
However that may be restrictive for FTR_EXACT, as we the safe
value would be set to "ftr->safe_val". I guess that may be better
than forcing to use an unsafe value for the boot CPU, which could
anyway conflict with the other CPUs and eventually trigger the
ftr alue to be safe_val.
I like the idea of using the helper, as it cleanups up the code a bit.
However, not being to set a feature to a certain value could be
restrictive,
as in general, it means that we can only disable a feature and not
adjust
its level of support.
Take PMUVER for example: with the helper, I can't override it from v8.4
to
v8.1. I can only go to v8.0.
Actually, we can only *disable* the PMU altogether. Same question
though...
M.
Is it something we care about?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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