[PATCH v3 0/2] riscv: Extension parsing fixes

[PATCH v3 0/2] riscv: Extension parsing fixes

[Charlie Jenkins]

This series contains two minor fixes for the extension parsing in
cpufeature.c.

Some T-Head boards without vector 1.0 support report "v" in the isa
string in their DT which will cause the kernel to run vector code. The
code to blacklist "v" from these boards was doing so by using
riscv_cached_mvendorid() which has not been populated at the time of
extension parsing. This fix instead greedily reads the mvendorid CSR of
the boot hart to determine if the cpu is from T-Head.

The other fix is for an incorrect indexing bug. riscv extensions
sometimes imply other extensions. When adding these "subset" extensions
to the hardware capabilities array, they need to be checked if they are
valid. The current code only checks if the extension that is including
other extensions is valid and not the subset extensions.  

These patches were previously included in:
https://lore.kernel.org/lkml/20240420-dev-charlie-support_thead_vector_6_9-v3-0-67cff4271d1d@rivosinc.com/

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
---
Changes in v3:
- Change comment about assuming all harts have the same vendorid/archid,
  to just state that only the boot hart is probed.
- Link to v2: https://lore.kernel.org/r/20240426-cpufeature_fixes-v2-0-7377442b1327@rivosinc.com

Changes in v2:
- Move comment about assuming all harts to have the same vendorid/archid
  to apply specifically to the code that expects that (Drew)
- Link to v1: https://lore.kernel.org/r/20240424-cpufeature_fixes-v1-0-585e73d2226b@rivosinc.com

---
Charlie Jenkins (2):
      riscv: cpufeature: Fix thead vector hwcap removal
      riscv: cpufeature: Fix extension subset checking

 arch/riscv/include/asm/sbi.h   |  2 ++
 arch/riscv/kernel/cpu.c        | 40 ++++++++++++++++++++++++++++++++++++----
 arch/riscv/kernel/cpufeature.c | 12 +++++++++---
 3 files changed, 47 insertions(+), 7 deletions(-)
---
base-commit: ed30a4a51bb196781c8058073ea720133a65596f
change-id: 20240424-cpufeature_fixes-91bec4d793e7
-- 
- Charlie

[PATCH v3 1/2] riscv: cpufeature: Fix thead vector hwcap removal

[Charlie Jenkins]

The riscv_cpuinfo struct that contains mvendorid and marchid is not
populated until all harts are booted which happens after the DT parsing.
Use the mvendorid/marchid from the boot hart to determine if the DT
contains an invalid V.

Fixes: d82f32202e0d ("RISC-V: Ignore V from the riscv,isa DT property on older T-Head CPUs")
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
---
 arch/riscv/include/asm/sbi.h   |  2 ++
 arch/riscv/kernel/cpu.c        | 40 ++++++++++++++++++++++++++++++++++++----
 arch/riscv/kernel/cpufeature.c | 10 ++++++++--
 3 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 6e68f8dff76b..0fab508a65b3 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -370,6 +370,8 @@ static inline int sbi_remote_fence_i(const struct cpumask *cpu_mask) { return -1
 static inline void sbi_init(void) {}
 #endif /* CONFIG_RISCV_SBI */
 
+unsigned long riscv_get_mvendorid(void);
+unsigned long riscv_get_marchid(void);
 unsigned long riscv_cached_mvendorid(unsigned int cpu_id);
 unsigned long riscv_cached_marchid(unsigned int cpu_id);
 unsigned long riscv_cached_mimpid(unsigned int cpu_id);
diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index d11d6320fb0d..c1f3655238fd 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -139,6 +139,34 @@ int riscv_of_parent_hartid(struct device_node *node, unsigned long *hartid)
 	return -1;
 }
 
+unsigned long __init riscv_get_marchid(void)
+{
+	struct riscv_cpuinfo *ci = this_cpu_ptr(&riscv_cpuinfo);
+
+#if IS_ENABLED(CONFIG_RISCV_SBI)
+	ci->marchid = sbi_spec_is_0_1() ? 0 : sbi_get_marchid();
+#elif IS_ENABLED(CONFIG_RISCV_M_MODE)
+	ci->marchid = csr_read(CSR_MARCHID);
+#else
+	ci->marchid = 0;
+#endif
+	return ci->marchid;
+}
+
+unsigned long __init riscv_get_mvendorid(void)
+{
+	struct riscv_cpuinfo *ci = this_cpu_ptr(&riscv_cpuinfo);
+
+#if IS_ENABLED(CONFIG_RISCV_SBI)
+	ci->mvendorid = sbi_spec_is_0_1() ? 0 : sbi_get_mvendorid();
+#elif IS_ENABLED(CONFIG_RISCV_M_MODE)
+	ci->mvendorid = csr_read(CSR_MVENDORID);
+#else
+	ci->mvendorid = 0;
+#endif
+	return ci->mvendorid;
+}
+
 DEFINE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
 
 unsigned long riscv_cached_mvendorid(unsigned int cpu_id)
@@ -170,12 +198,16 @@ static int riscv_cpuinfo_starting(unsigned int cpu)
 	struct riscv_cpuinfo *ci = this_cpu_ptr(&riscv_cpuinfo);
 
 #if IS_ENABLED(CONFIG_RISCV_SBI)
-	ci->mvendorid = sbi_spec_is_0_1() ? 0 : sbi_get_mvendorid();
-	ci->marchid = sbi_spec_is_0_1() ? 0 : sbi_get_marchid();
+	if (!ci->mvendorid)
+		ci->mvendorid = sbi_spec_is_0_1() ? 0 : sbi_get_mvendorid();
+	if (!ci->marchid)
+		ci->marchid = sbi_spec_is_0_1() ? 0 : sbi_get_marchid();
 	ci->mimpid = sbi_spec_is_0_1() ? 0 : sbi_get_mimpid();
 #elif IS_ENABLED(CONFIG_RISCV_M_MODE)
-	ci->mvendorid = csr_read(CSR_MVENDORID);
-	ci->marchid = csr_read(CSR_MARCHID);
+	if (!ci->mvendorid)
+		ci->mvendorid = csr_read(CSR_MVENDORID);
+	if (!ci->marchid)
+		ci->marchid = csr_read(CSR_MARCHID);
 	ci->mimpid = csr_read(CSR_MIMPID);
 #else
 	ci->mvendorid = 0;
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 3ed2359eae35..818adb0d388e 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -490,6 +490,8 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
 	struct acpi_table_header *rhct;
 	acpi_status status;
 	unsigned int cpu;
+	u64 boot_vendorid;
+	u64 boot_archid;
 
 	if (!acpi_disabled) {
 		status = acpi_get_table(ACPI_SIG_RHCT, 0, &rhct);
@@ -497,6 +499,9 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
 			return;
 	}
 
+	boot_vendorid = riscv_get_mvendorid();
+	boot_archid = riscv_get_marchid();
+
 	for_each_possible_cpu(cpu) {
 		struct riscv_isainfo *isainfo = &hart_isa[cpu];
 		unsigned long this_hwcap = 0;
@@ -543,9 +548,10 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
 		 * version of the vector specification put "v" into their DTs.
 		 * CPU cores with the ratified spec will contain non-zero
 		 * marchid.
+		 *
+		 * Disable vector if the boot hart has a T-Head mvendorid and an marchid of 0.
 		 */
-		if (acpi_disabled && riscv_cached_mvendorid(cpu) == THEAD_VENDOR_ID &&
-		    riscv_cached_marchid(cpu) == 0x0) {
+		if (acpi_disabled && boot_vendorid == THEAD_VENDOR_ID && boot_archid == 0x0) {
 			this_hwcap &= ~isa2hwcap[RISCV_ISA_EXT_v];
 			clear_bit(RISCV_ISA_EXT_v, isainfo->isa);
 		}

-- 
2.44.0

[PATCH v3 2/2] riscv: cpufeature: Fix extension subset checking

[Charlie Jenkins]

This loop is supposed to check if ext->subset_ext_ids[j] is valid, rather
than if ext->subset_ext_ids[i] is valid, before setting the extension
id ext->subset_ext_ids[j] in isainfo->isa.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Fixes: 0d8295ed975b ("riscv: add ISA extension parsing for scalar crypto")
---
 arch/riscv/kernel/cpufeature.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 818adb0d388e..ab683bed8d44 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -605,7 +605,7 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
 
 			if (ext->subset_ext_size) {
 				for (int j = 0; j < ext->subset_ext_size; j++) {
-					if (riscv_isa_extension_check(ext->subset_ext_ids[i]))
+					if (riscv_isa_extension_check(ext->subset_ext_ids[j]))
 						set_bit(ext->subset_ext_ids[j], isainfo->isa);
 				}
 			}

-- 
2.44.0

Re: [PATCH v3 1/2] riscv: cpufeature: Fix thead vector hwcap removal

[Andrew Jones]

On Mon, Apr 29, 2024 at 03:29:51PM GMT, Charlie Jenkins wrote:
...
> +		 *
> +		 * Disable vector if the boot hart has a T-Head mvendorid and an marchid of 0.

I probably would have added the 'why' to this comment, i.e. T-Head doesn't
have standard V so things will break if we try to use it, or whatever. The
'what' alone is just putting the easy to read condition below into
English, making it an unnecessary comment.

Thanks,
drew

>  		 */
> -		if (acpi_disabled && riscv_cached_mvendorid(cpu) == THEAD_VENDOR_ID &&
> -		    riscv_cached_marchid(cpu) == 0x0) {
> +		if (acpi_disabled && boot_vendorid == THEAD_VENDOR_ID && boot_archid == 0x0) {
>  			this_hwcap &= ~isa2hwcap[RISCV_ISA_EXT_v];
>  			clear_bit(RISCV_ISA_EXT_v, isainfo->isa);
>  		}
> 
> -- 
> 2.44.0
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH v3 1/2] riscv: cpufeature: Fix thead vector hwcap removal

[Charlie Jenkins]

On Tue, Apr 30, 2024 at 12:07:26PM +0200, Andrew Jones wrote:
> On Mon, Apr 29, 2024 at 03:29:51PM GMT, Charlie Jenkins wrote:
> ...
> > +		 *
> > +		 * Disable vector if the boot hart has a T-Head mvendorid and an marchid of 0.
> 
> I probably would have added the 'why' to this comment, i.e. T-Head doesn't
> have standard V so things will break if we try to use it, or whatever. The
> 'what' alone is just putting the easy to read condition below into
> English, making it an unnecessary comment.

The 'why' is directly above this comment. I'll just get rid of this
addition.

- Charlie

> 
> Thanks,
> drew
> 
> >  		 */
> > -		if (acpi_disabled && riscv_cached_mvendorid(cpu) == THEAD_VENDOR_ID &&
> > -		    riscv_cached_marchid(cpu) == 0x0) {
> > +		if (acpi_disabled && boot_vendorid == THEAD_VENDOR_ID && boot_archid == 0x0) {
> >  			this_hwcap &= ~isa2hwcap[RISCV_ISA_EXT_v];
> >  			clear_bit(RISCV_ISA_EXT_v, isainfo->isa);
> >  		}
> > 
> > -- 
> > 2.44.0
> > 
> > 
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv