* [PATCH v2 1/3] arm64/hwcap: Add hwcap for FEAT_LSFE
2025-07-03 16:23 [PATCH v2 0/3] arm64: Support FEAT_LSFE (Large System Float Extension) Mark Brown
@ 2025-07-03 16:23 ` Mark Brown
2025-07-03 16:23 ` [PATCH v2 2/3] KVM: arm64: Expose FEAT_LSFE to guests Mark Brown
2025-07-03 16:23 ` [PATCH v2 3/3] kselftest/arm64: Add lsfe to the hwcaps test Mark Brown
2 siblings, 0 replies; 4+ messages in thread
From: Mark Brown @ 2025-07-03 16:23 UTC (permalink / raw)
To: Catalin Marinas, Will Deacon, Jonathan Corbet, Marc Zyngier,
Oliver Upton, Joey Gouly, Suzuki K Poulose, Shuah Khan
Cc: linux-arm-kernel, linux-doc, linux-kernel, kvmarm,
linux-kselftest, Mark Brown
FEAT_LSFE (Large System Float Extension), providing atomic floating point
memory operations, is optional from v9.5. This feature adds no new
architectural stare and we have no immediate use for it in the kernel so
simply provide a hwcap for it to support discovery by userspace.
Signed-off-by: Mark Brown <broonie@kernel.org>
---
Documentation/arch/arm64/elf_hwcaps.rst | 4 ++++
arch/arm64/include/asm/hwcap.h | 1 +
arch/arm64/include/uapi/asm/hwcap.h | 1 +
arch/arm64/kernel/cpufeature.c | 2 ++
arch/arm64/kernel/cpuinfo.c | 1 +
5 files changed, 9 insertions(+)
diff --git a/Documentation/arch/arm64/elf_hwcaps.rst b/Documentation/arch/arm64/elf_hwcaps.rst
index 69d7afe56853..aafb969ca263 100644
--- a/Documentation/arch/arm64/elf_hwcaps.rst
+++ b/Documentation/arch/arm64/elf_hwcaps.rst
@@ -435,6 +435,10 @@ HWCAP2_SME_SF8DP4
HWCAP2_POE
Functionality implied by ID_AA64MMFR3_EL1.S1POE == 0b0001.
+HWCAP3_LSFE
+ Functionality implied by ID_AA64ISAR3_EL1.LSFE == 0b0001
+
+
4. Unused AT_HWCAP bits
-----------------------
diff --git a/arch/arm64/include/asm/hwcap.h b/arch/arm64/include/asm/hwcap.h
index 1c3f9617d54f..f8d02c14e5a2 100644
--- a/arch/arm64/include/asm/hwcap.h
+++ b/arch/arm64/include/asm/hwcap.h
@@ -176,6 +176,7 @@
#define KERNEL_HWCAP_POE __khwcap2_feature(POE)
#define __khwcap3_feature(x) (const_ilog2(HWCAP3_ ## x) + 128)
+#define KERNEL_HWCAP_LSFE __khwcap3_feature(LSFE)
/*
* This yields a mask that user programs can use to figure out what
diff --git a/arch/arm64/include/uapi/asm/hwcap.h b/arch/arm64/include/uapi/asm/hwcap.h
index 705a7afa8e58..339b9dbf7cfc 100644
--- a/arch/arm64/include/uapi/asm/hwcap.h
+++ b/arch/arm64/include/uapi/asm/hwcap.h
@@ -143,5 +143,6 @@
/*
* HWCAP3 flags - for AT_HWCAP3
*/
+#define HWCAP3_LSFE (1 << 0)
#endif /* _UAPI__ASM_HWCAP_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index b34044e20128..726054ac8091 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -278,6 +278,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar2[] = {
static const struct arm64_ftr_bits ftr_id_aa64isar3[] = {
ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_FPRCVT_SHIFT, 4, 0),
+ ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_LSFE_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_FAMINMAX_SHIFT, 4, 0),
ARM64_FTR_END,
};
@@ -3175,6 +3176,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
HWCAP_CAP(ID_AA64ISAR1_EL1, I8MM, IMP, CAP_HWCAP, KERNEL_HWCAP_I8MM),
HWCAP_CAP(ID_AA64ISAR2_EL1, LUT, IMP, CAP_HWCAP, KERNEL_HWCAP_LUT),
HWCAP_CAP(ID_AA64ISAR3_EL1, FAMINMAX, IMP, CAP_HWCAP, KERNEL_HWCAP_FAMINMAX),
+ HWCAP_CAP(ID_AA64ISAR3_EL1, LSFE, IMP, CAP_HWCAP, KERNEL_HWCAP_LSFE),
HWCAP_CAP(ID_AA64MMFR2_EL1, AT, IMP, CAP_HWCAP, KERNEL_HWCAP_USCAT),
#ifdef CONFIG_ARM64_SVE
HWCAP_CAP(ID_AA64PFR0_EL1, SVE, IMP, CAP_HWCAP, KERNEL_HWCAP_SVE),
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index c1f2b6b04b41..2a1efe8e1fdf 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -160,6 +160,7 @@ static const char *const hwcap_str[] = {
[KERNEL_HWCAP_SME_SFEXPA] = "smesfexpa",
[KERNEL_HWCAP_SME_STMOP] = "smestmop",
[KERNEL_HWCAP_SME_SMOP4] = "smesmop4",
+ [KERNEL_HWCAP_LSFE] = "lsfe",
};
#ifdef CONFIG_COMPAT
--
2.39.5
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH v2 2/3] KVM: arm64: Expose FEAT_LSFE to guests
2025-07-03 16:23 [PATCH v2 0/3] arm64: Support FEAT_LSFE (Large System Float Extension) Mark Brown
2025-07-03 16:23 ` [PATCH v2 1/3] arm64/hwcap: Add hwcap for FEAT_LSFE Mark Brown
@ 2025-07-03 16:23 ` Mark Brown
2025-07-03 16:23 ` [PATCH v2 3/3] kselftest/arm64: Add lsfe to the hwcaps test Mark Brown
2 siblings, 0 replies; 4+ messages in thread
From: Mark Brown @ 2025-07-03 16:23 UTC (permalink / raw)
To: Catalin Marinas, Will Deacon, Jonathan Corbet, Marc Zyngier,
Oliver Upton, Joey Gouly, Suzuki K Poulose, Shuah Khan
Cc: linux-arm-kernel, linux-doc, linux-kernel, kvmarm,
linux-kselftest, Mark Brown
FEAT_LSFE (Large System Float Extension), providing atomic floating point
memory operations, is optional from v9.5. This feature adds no new
architectural state, expose the relevant ID register field to guests so
they can discover it.
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/kvm/sys_regs.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 76c2f0da821f..be685422bf9b 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1636,7 +1636,8 @@ static u64 __kvm_read_sanitised_id_reg(const struct kvm_vcpu *vcpu,
val &= ~ARM64_FEATURE_MASK(ID_AA64ISAR2_EL1_WFxT);
break;
case SYS_ID_AA64ISAR3_EL1:
- val &= ID_AA64ISAR3_EL1_FPRCVT | ID_AA64ISAR3_EL1_FAMINMAX;
+ val &= ID_AA64ISAR3_EL1_FPRCVT | ID_AA64ISAR3_EL1_LSFE |
+ ID_AA64ISAR3_EL1_FAMINMAX;
break;
case SYS_ID_AA64MMFR2_EL1:
val &= ~ID_AA64MMFR2_EL1_CCIDX_MASK;
@@ -2921,6 +2922,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
ID_AA64ISAR2_EL1_APA3 |
ID_AA64ISAR2_EL1_GPA3)),
ID_WRITABLE(ID_AA64ISAR3_EL1, (ID_AA64ISAR3_EL1_FPRCVT |
+ ID_AA64ISAR3_EL1_LSFE |
ID_AA64ISAR3_EL1_FAMINMAX)),
ID_UNALLOCATED(6,4),
ID_UNALLOCATED(6,5),
--
2.39.5
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH v2 3/3] kselftest/arm64: Add lsfe to the hwcaps test
2025-07-03 16:23 [PATCH v2 0/3] arm64: Support FEAT_LSFE (Large System Float Extension) Mark Brown
2025-07-03 16:23 ` [PATCH v2 1/3] arm64/hwcap: Add hwcap for FEAT_LSFE Mark Brown
2025-07-03 16:23 ` [PATCH v2 2/3] KVM: arm64: Expose FEAT_LSFE to guests Mark Brown
@ 2025-07-03 16:23 ` Mark Brown
2 siblings, 0 replies; 4+ messages in thread
From: Mark Brown @ 2025-07-03 16:23 UTC (permalink / raw)
To: Catalin Marinas, Will Deacon, Jonathan Corbet, Marc Zyngier,
Oliver Upton, Joey Gouly, Suzuki K Poulose, Shuah Khan
Cc: linux-arm-kernel, linux-doc, linux-kernel, kvmarm,
linux-kselftest, Mark Brown
This feature has no traps associated with it so the SIGILL is not reliable.
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/arm64/abi/hwcap.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/tools/testing/selftests/arm64/abi/hwcap.c b/tools/testing/selftests/arm64/abi/hwcap.c
index 35f521e5f41c..faa0f82f27e0 100644
--- a/tools/testing/selftests/arm64/abi/hwcap.c
+++ b/tools/testing/selftests/arm64/abi/hwcap.c
@@ -17,6 +17,8 @@
#include <asm/sigcontext.h>
#include <asm/unistd.h>
+#include <linux/auxvec.h>
+
#include "../../kselftest.h"
#define TESTS_PER_HWCAP 3
@@ -165,6 +167,18 @@ static void lse128_sigill(void)
: "cc", "memory");
}
+static void lsfe_sigill(void)
+{
+ float __attribute__ ((aligned (16))) mem = 0;
+ register float *memp asm ("x0") = &mem;
+
+ /* LDFADD H0, H0, [X0] */
+ asm volatile(".inst 0x7c200000"
+ : "+r" (memp)
+ :
+ : "cc", "memory");
+}
+
static void lut_sigill(void)
{
/* LUTI2 V0.16B, { V0.16B }, V[0] */
@@ -758,6 +772,13 @@ static const struct hwcap_data {
.cpuinfo = "lse128",
.sigill_fn = lse128_sigill,
},
+ {
+ .name = "LSFE",
+ .at_hwcap = AT_HWCAP3,
+ .hwcap_bit = HWCAP3_LSFE,
+ .cpuinfo = "lsfe",
+ .sigill_fn = lsfe_sigill,
+ },
{
.name = "LUT",
.at_hwcap = AT_HWCAP2,
--
2.39.5
^ permalink raw reply related [flat|nested] 4+ messages in thread