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Subject[PATCH 2/2] arm64: Support systems without FP/ASIMD
Date
The arm64 kernel assumes that FP/ASIMD units are always present
and accesses the FP/ASIMD specific registers unconditionally. This
could cause problems when they are absent. This patch adds the
support for kernel handling systems without FP/ASIMD by skipping the
register access within the kernel. For kvm, we trap the accesses
to FP/ASIMD and inject an undefined instruction exception to the VM.

The callers of the exported kernel_neon_begin_parital() should
make sure that the FP/ASIMD is supported.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
---
arch/arm64/crypto/aes-ce-ccm-glue.c | 2 +-
arch/arm64/crypto/aes-ce-cipher.c | 2 ++
arch/arm64/crypto/ghash-ce-glue.c | 2 ++
arch/arm64/crypto/sha1-ce-glue.c | 2 ++
arch/arm64/include/asm/cpufeature.h | 8 +++++++-
arch/arm64/include/asm/neon.h | 3 ++-
arch/arm64/kernel/cpufeature.c | 15 +++++++++++++++
arch/arm64/kernel/fpsimd.c | 14 ++++++++++++++
arch/arm64/kvm/handle_exit.c | 11 +++++++++++
arch/arm64/kvm/hyp/hyp-entry.S | 9 ++++++++-
arch/arm64/kvm/hyp/switch.c | 5 ++++-
11 files changed, 68 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/crypto/aes-ce-ccm-glue.c b/arch/arm64/crypto/aes-ce-ccm-glue.c
index f4bf2f2..d001b4e 100644
--- a/arch/arm64/crypto/aes-ce-ccm-glue.c
+++ b/arch/arm64/crypto/aes-ce-ccm-glue.c
@@ -296,7 +296,7 @@ static struct aead_alg ccm_aes_alg = {

static int __init aes_mod_init(void)
{
- if (!(elf_hwcap & HWCAP_AES))
+ if (!(elf_hwcap & HWCAP_AES) || !system_supports_fpsimd())
return -ENODEV;
return crypto_register_aead(&ccm_aes_alg);
}
diff --git a/arch/arm64/crypto/aes-ce-cipher.c b/arch/arm64/crypto/aes-ce-cipher.c
index f7bd9bf..1a43be2 100644
--- a/arch/arm64/crypto/aes-ce-cipher.c
+++ b/arch/arm64/crypto/aes-ce-cipher.c
@@ -253,6 +253,8 @@ static struct crypto_alg aes_alg = {

static int __init aes_mod_init(void)
{
+ if (!system_supports_fpsimd())
+ return -ENODEV;
return crypto_register_alg(&aes_alg);
}

diff --git a/arch/arm64/crypto/ghash-ce-glue.c b/arch/arm64/crypto/ghash-ce-glue.c
index 833ec1e..2bc518d 100644
--- a/arch/arm64/crypto/ghash-ce-glue.c
+++ b/arch/arm64/crypto/ghash-ce-glue.c
@@ -144,6 +144,8 @@ static struct shash_alg ghash_alg = {

static int __init ghash_ce_mod_init(void)
{
+ if (!system_supports_fpsimd())
+ return -ENODEV;
return crypto_register_shash(&ghash_alg);
}

diff --git a/arch/arm64/crypto/sha1-ce-glue.c b/arch/arm64/crypto/sha1-ce-glue.c
index aefda98..9f3427a 100644
--- a/arch/arm64/crypto/sha1-ce-glue.c
+++ b/arch/arm64/crypto/sha1-ce-glue.c
@@ -102,6 +102,8 @@ static struct shash_alg alg = {

static int __init sha1_ce_mod_init(void)
{
+ if (!system_supports_fpsimd())
+ return -ENODEV;
return crypto_register_shash(&alg);
}

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index ae5e994..63d739c 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -38,8 +38,9 @@
#define ARM64_HAS_32BIT_EL0 13
#define ARM64_HYP_OFFSET_LOW 14
#define ARM64_MISMATCHED_CACHE_LINE_SIZE 15
+#define ARM64_HAS_NO_FPSIMD 16

-#define ARM64_NCAPS 16
+#define ARM64_NCAPS 17

#ifndef __ASSEMBLY__

@@ -236,6 +237,11 @@ static inline bool system_supports_mixed_endian_el0(void)
return id_aa64mmfr0_mixed_endian_el0(read_system_reg(SYS_ID_AA64MMFR0_EL1));
}

+static inline bool system_supports_fpsimd(void)
+{
+ return !cpus_have_const_cap(ARM64_HAS_NO_FPSIMD);
+}
+
#endif /* __ASSEMBLY__ */

#endif
diff --git a/arch/arm64/include/asm/neon.h b/arch/arm64/include/asm/neon.h
index 13ce4cc..ad4cdc9 100644
--- a/arch/arm64/include/asm/neon.h
+++ b/arch/arm64/include/asm/neon.h
@@ -9,8 +9,9 @@
*/

#include <linux/types.h>
+#include <asm/fpsimd.h>

-#define cpu_has_neon() (1)
+#define cpu_has_neon() system_supports_fpsimd()

#define kernel_neon_begin() kernel_neon_begin_partial(32)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index d577f26..8f22544 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -744,6 +744,14 @@ static bool hyp_offset_low(const struct arm64_cpu_capabilities *entry,
return idmap_addr > GENMASK(VA_BITS - 2, 0) && !is_kernel_in_hyp_mode();
}

+static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unused)
+{
+ u64 pfr0 = read_system_reg(SYS_ID_AA64PFR0_EL1);
+
+ return cpuid_feature_extract_signed_field(pfr0,
+ ID_AA64PFR0_FP_SHIFT) < 0;
+}
+
static const struct arm64_cpu_capabilities arm64_features[] = {
{
.desc = "GIC system register CPU interface",
@@ -827,6 +835,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.def_scope = SCOPE_SYSTEM,
.matches = hyp_offset_low,
},
+ {
+ /* FP/SIMD is not implemented */
+ .capability = ARM64_HAS_NO_FPSIMD,
+ .def_scope = SCOPE_SYSTEM,
+ .min_field_value = 0,
+ .matches = has_no_fpsimd,
+ },
{},
};

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 975b274..80da5aa 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -127,6 +127,8 @@ void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)

void fpsimd_thread_switch(struct task_struct *next)
{
+ if (!system_supports_fpsimd())
+ return;
/*
* Save the current FPSIMD state to memory, but only if whatever is in
* the registers is in fact the most recent userland FPSIMD state of
@@ -157,6 +159,8 @@ void fpsimd_thread_switch(struct task_struct *next)

void fpsimd_flush_thread(void)
{
+ if (!system_supports_fpsimd())
+ return;
memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
fpsimd_flush_task_state(current);
set_thread_flag(TIF_FOREIGN_FPSTATE);
@@ -168,6 +172,8 @@ void fpsimd_flush_thread(void)
*/
void fpsimd_preserve_current_state(void)
{
+ if (!system_supports_fpsimd())
+ return;
preempt_disable();
if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
fpsimd_save_state(&current->thread.fpsimd_state);
@@ -181,6 +187,8 @@ void fpsimd_preserve_current_state(void)
*/
void fpsimd_restore_current_state(void)
{
+ if (!system_supports_fpsimd())
+ return;
preempt_disable();
if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
struct fpsimd_state *st = &current->thread.fpsimd_state;
@@ -199,6 +207,8 @@ void fpsimd_restore_current_state(void)
*/
void fpsimd_update_current_state(struct fpsimd_state *state)
{
+ if (!system_supports_fpsimd())
+ return;
preempt_disable();
fpsimd_load_state(state);
if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
@@ -228,6 +238,8 @@ static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate);
*/
void kernel_neon_begin_partial(u32 num_regs)
{
+ if (WARN_ON(!system_supports_fpsimd()))
+ return;
if (in_interrupt()) {
struct fpsimd_partial_state *s = this_cpu_ptr(
in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
@@ -252,6 +264,8 @@ EXPORT_SYMBOL(kernel_neon_begin_partial);

void kernel_neon_end(void)
{
+ if (!system_supports_fpsimd())
+ return;
if (in_interrupt()) {
struct fpsimd_partial_state *s = this_cpu_ptr(
in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index fa96fe2..39e055a 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -57,6 +57,16 @@ static int handle_smc(struct kvm_vcpu *vcpu, struct kvm_run *run)
return 1;
}

+/*
+ * Guest access to FP/ASIMD registers are routed to this handler only
+ * when the system doesn't support FP/ASIMD.
+ */
+static int handle_no_fpsimd(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+ kvm_inject_undefined(vcpu);
+ return 1;
+}
+
/**
* kvm_handle_wfx - handle a wait-for-interrupts or wait-for-event
* instruction executed by a guest
@@ -144,6 +154,7 @@ static exit_handle_fn arm_exit_handlers[] = {
[ESR_ELx_EC_BREAKPT_LOW]= kvm_handle_guest_debug,
[ESR_ELx_EC_BKPT32] = kvm_handle_guest_debug,
[ESR_ELx_EC_BRK64] = kvm_handle_guest_debug,
+ [ESR_ELx_EC_FP_ASIMD] = handle_no_fpsimd,
};

static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index f6d9694..16167d7 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -117,9 +117,16 @@ el1_trap:
* x2: ESR_EC
*/

- /* Guest accessed VFP/SIMD registers, save host, restore Guest */
+ /*
+ * We trap the first access to the FP/SIMD to save the host context
+ * and restore the guest context lazily.
+ * If FP/SIMD is not implemented, handle the trap and inject an
+ * undefined instruction exception to the guest.
+ */
+alternative_if_not ARM64_HAS_NO_FPSIMD
cmp x2, #ESR_ELx_EC_FP_ASIMD
b.eq __fpsimd_guest_restore
+alternative_else_nop_endif

mrs x0, tpidr_el2
mov x1, #ARM_EXCEPTION_TRAP
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index ae7855f..f2d0c4f 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -18,6 +18,7 @@
#include <linux/types.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_hyp.h>
+#include <asm/fpsimd.h>

static bool __hyp_text __fpsimd_enabled_nvhe(void)
{
@@ -73,9 +74,11 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
* traps are only taken to EL2 if the operation would not otherwise
* trap to EL1. Therefore, always make sure that for 32-bit guests,
* we set FPEXC.EN to prevent traps to EL1, when setting the TFP bit.
+ * If FP/ASIMD is not implemented, FPEXC is UNDEFINED and any access to
+ * it will cause an exception.
*/
val = vcpu->arch.hcr_el2;
- if (!(val & HCR_RW)) {
+ if (!(val & HCR_RW) && system_supports_fpsimd()) {
write_sysreg(1 << 30, fpexc32_el2);
isb();
}
--
2.7.4
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