Messages in this thread | | | Subject | Re: [PATCH v4 10/21] arm64: cpufeature: Use IDreg override in __read_sysreg_by_encoding() | From | Suzuki K Poulose <> | Date | Sat, 23 Jan 2021 16:04:26 +0000 |
| |
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@kernel.org>
>> 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@arm.com>
| |