On 1/22/21 6:53 PM, Catalin Marinas wrote:
On Mon, Jan 18, 2021 at 09:45:22AM +0000, Marc Zyngier wrote:
__read_sysreg_by_encoding() is used by a bunch of cpufeature helpers,
which should take the feature override into account. Let's do that.
For a good measure (and because we are likely to need to further
down the line), make this helper available to the rest of the
non-modular kernel.
Code that needs to know the *real* features of a CPU can still
use read_sysreg_s(), and find the bare, ugly truth.
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index aaa075c6f029..48a011935d8c 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1149,14 +1149,17 @@ u64 read_sanitised_ftr_reg(u32 id)
EXPORT_SYMBOL_GPL(read_sanitised_ftr_reg);
#define read_sysreg_case(r) \
- case r: return read_sysreg_s(r)
+ case r: val = read_sysreg_s(r); break;
/*
* __read_sysreg_by_encoding() - Used by a STARTING cpu before cpuinfo is populated.
* Read the system register on the current CPU
*/
-static u64 __read_sysreg_by_encoding(u32 sys_id)
+u64 __read_sysreg_by_encoding(u32 sys_id)
{
+ struct arm64_ftr_reg *regp;
+ u64 val;
+
switch (sys_id) {
read_sysreg_case(SYS_ID_PFR0_EL1);
read_sysreg_case(SYS_ID_PFR1_EL1);
@@ -1199,6 +1202,14 @@ static u64 __read_sysreg_by_encoding(u32 sys_id)
BUG();
return 0;
}
+
+ regp = get_arm64_ftr_reg(sys_id);
+ if (regp && regp->override_mask && regp->override_val) {
+ val &= ~*regp->override_mask;
+ val |= (*regp->override_val & *regp->override_mask);
+ }
+
+ return val;
Ah, now the previous patch makes more sense. I don't particularly like
this but I can't tell how to work around it. I was hoping that the
overriding feature behaves more like a secondary CPU that limits all the
overridden features. However, this approach would fail for FTR_EXACT
cases (like PAC, though I wonder whether it fails already with your
previous patch since the boot CPU value won't match the override, hence
dropping to the safe one).
Correct !For FTR_EXACT, we dont want to override a value that is not safe, e.g PAC.
This is handled correctly in the previous patch and thus we are covered.
Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
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