Re: [PATCH v4 10/21] arm64: cpufeature: Use IDreg override in __read_sysreg_by_encoding()
On 1/22/21 6:53 PM, Catalin Marinas wrote:
On Mon, Jan 18, 2021 at 09:45:22AM +, 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
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
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Re: [PATCH v4 10/21] arm64: cpufeature: Use IDreg override in __read_sysreg_by_encoding()
On Mon, Jan 18, 2021 at 09:45:22AM +, 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
> ---
> arch/arm64/include/asm/cpufeature.h | 1 +
> arch/arm64/kernel/cpufeature.c | 15 +--
> 2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h
> b/arch/arm64/include/asm/cpufeature.h
> index 465d2cb63bfc..fe0130d6c0ff 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -602,6 +602,7 @@ void __init setup_cpu_features(void);
> void check_local_cpu_capabilities(void);
>
> u64 read_sanitised_ftr_reg(u32 id);
> +u64 __read_sysreg_by_encoding(u32 sys_id);
>
> static inline bool cpu_supports_mixed_endian_el0(void)
> {
> 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).
--
Catalin
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[PATCH v4 10/21] arm64: cpufeature: Use IDreg override in __read_sysreg_by_encoding()
__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
---
arch/arm64/include/asm/cpufeature.h | 1 +
arch/arm64/kernel/cpufeature.c | 15 +--
2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/cpufeature.h
b/arch/arm64/include/asm/cpufeature.h
index 465d2cb63bfc..fe0130d6c0ff 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -602,6 +602,7 @@ void __init setup_cpu_features(void);
void check_local_cpu_capabilities(void);
u64 read_sanitised_ftr_reg(u32 id);
+u64 __read_sysreg_by_encoding(u32 sys_id);
static inline bool cpu_supports_mixed_endian_el0(void)
{
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;
}
#include
--
2.29.2
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