[PATCH v14 15/39] arm64/sme: Implement ZA context switching

Mark Brown
2022-04-19T11:24:35Z

Allocate space for storing ZA on first access to SME and use that to save
and restore ZA state when context switching. We do this by using the vector
form of the LDR and STR ZA instructions, these do not require streaming
mode and have implementation recommendations that they avoid contention
issues in shared SMCU implementations.

Since ZA is architecturally guaranteed to be zeroed when enabled we do not
need to explicitly zero ZA, either we will be restoring from a saved copy
or trapping on first use of SME so we know that ZA must be disabled.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/include/asm/fpsimd.h | 5 ++++-
arch/arm64/include/asm/fpsimdmacros.h | 22 ++++++++++++++++++++++
arch/arm64/include/asm/kvm_host.h | 3 +++
arch/arm64/include/asm/processor.h | 1 +
arch/arm64/kernel/entry-fpsimd.S | 22 ++++++++++++++++++++++
arch/arm64/kernel/fpsimd.c | 20 +++++++++++++-------
arch/arm64/kvm/fpsimd.c | 2 +-
7 files changed, 66 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
index cd94f5c5b516..1a709c03bb6c 100644
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -47,7 +47,8 @@ extern void fpsimd_update_current_state(struct user_fpsimd_state const *state);

extern void fpsimd_bind_state_to_cpu(struct user_fpsimd_state *state,
void *sve_state, unsigned int sve_vl,
- unsigned int sme_vl, u64 *svcr);
+ void *za_state, unsigned int sme_vl,
+ u64 *svcr);

extern void fpsimd_flush_task_state(struct task_struct *target);
extern void fpsimd_save_and_flush_cpu_state(void);
@@ -90,6 +91,8 @@ extern void sve_flush_live(bool flush_ffr, unsigned long vq_minus_1);
extern unsigned int sve_get_vl(void);
extern void sve_set_vq(unsigned long vq_minus_1);
extern void sme_set_vq(unsigned long vq_minus_1);
+extern void za_save_state(void *state);
+extern void za_load_state(void const *state);

struct arm64_cpu_capabilities;
extern void sve_kernel_enable(const struct arm64_cpu_capabilities *__unused);
diff --git a/arch/arm64/include/asm/fpsimdmacros.h b/arch/arm64/include/asm/fpsimdmacros.h
index f6ab36e0cd8d..5e0910cf4832 100644
--- a/arch/arm64/include/asm/fpsimdmacros.h
+++ b/arch/arm64/include/asm/fpsimdmacros.h
@@ -319,3 +319,25 @@
ldr w\nxtmp, [\xpfpsr, #4]
msr fpcr, x\nxtmp
.endm
+
+.macro sme_save_za nxbase, xvl, nw
+ mov w\nw, #0
+
+423:
+ _sme_str_zav \nw, \nxbase
+ add x\nxbase, x\nxbase, \xvl
+ add x\nw, x\nw, #1
+ cmp \xvl, x\nw
+ bne 423b
+.endm
+
+.macro sme_load_za nxbase, xvl, nw
+ mov w\nw, #0
+
+423:
+ _sme_ldr_zav \nw, \nxbase
+ add x\nxbase, x\nxbase, \xvl
+ add x\nw, x\nw, #1
+ cmp \xvl, x\nw
+ bne 423b
+.endm
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 94a27a7520f4..8a7c442d5b57 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -295,8 +295,11 @@ struct vcpu_reset_state {

struct kvm_vcpu_arch {
struct kvm_cpu_context ctxt;
+
+ /* Guest floating point state */
void *sve_state;
unsigned int sve_max_vl;
+ u64 svcr;

/* Stage 2 paging state used by the hardware on next switch */
struct kvm_s2_mmu *hw_mmu;
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 7542310b4e6b..6a3a6c3dec90 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -154,6 +154,7 @@ struct thread_struct {

unsigned int fpsimd_cpu;
void *sve_state; /* SVE registers, if any */
+ void *za_state; /* ZA register, if any */
unsigned int vl[ARM64_VEC_MAX]; /* vector length */
unsigned int vl_onexec[ARM64_VEC_MAX]; /* vl after next exec */
unsigned long fault_address; /* fault info */
diff --git a/arch/arm64/kernel/entry-fpsimd.S b/arch/arm64/kernel/entry-fpsimd.S
index 6f88c0f86d50..229436f33df5 100644
--- a/arch/arm64/kernel/entry-fpsimd.S
+++ b/arch/arm64/kernel/entry-fpsimd.S
@@ -99,4 +99,26 @@ SYM_FUNC_START(sme_set_vq)
ret
SYM_FUNC_END(sme_set_vq)

+/*
+ * Save the SME state
+ *
+ * x0 - pointer to buffer for state
+ */
+SYM_FUNC_START(za_save_state)
+ _sme_rdsvl 1, 1 // x1 = VL/8
+ sme_save_za 0, x1, 12
+ ret
+SYM_FUNC_END(za_save_state)
+
+/*
+ * Load the SME state
+ *
+ * x0 - pointer to buffer for state
+ */
+SYM_FUNC_START(za_load_state)
+ _sme_rdsvl 1, 1 // x1 = VL/8
+ sme_load_za 0, x1, 12
+ ret
+SYM_FUNC_END(za_load_state)
+
#endif /* CONFIG_ARM64_SME */
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index f8506a875eb2..dc38f3f2a28a 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -121,6 +121,7 @@
struct fpsimd_last_state_struct {
struct user_fpsimd_state *st;
void *sve_state;
+ void *za_state;
u64 *svcr;
unsigned int sve_vl;
unsigned int sme_vl;
@@ -387,11 +388,15 @@ static void task_fpsimd_load(void)
if (system_supports_sme()) {
unsigned long sme_vl = task_get_sme_vl(current);

+ /* Ensure VL is set up for restoring data */
if (test_thread_flag(TIF_SME))
sme_set_vq(sve_vq_from_vl(sme_vl) - 1);

write_sysreg_s(current->thread.svcr, SYS_SVCR_EL0);

+ if (thread_za_enabled(&current->thread))
+ za_load_state(current->thread.za_state);
+
if (thread_sm_enabled(&current->thread)) {
restore_sve_regs = true;
restore_ffr = system_supports_fa64();
@@ -441,11 +446,10 @@ static void fpsimd_save(void)
u64 *svcr = last->svcr;
*svcr = read_sysreg_s(SYS_SVCR_EL0);

- if (thread_za_enabled(&current->thread)) {
- /* ZA state managment is not implemented yet */
- force_signal_inject(SIGKILL, SI_KERNEL, 0, 0);
- return;
- }
+ *svcr = read_sysreg_s(SYS_SVCR_EL0);
+
+ if (*svcr & SYS_SVCR_EL0_ZA_MASK)
+ za_save_state(last->za_state);

/* If we are in streaming mode override regular SVE. */
if (*svcr & SYS_SVCR_EL0_SM_MASK) {
@@ -1483,6 +1487,7 @@ static void fpsimd_bind_task_to_cpu(void)
WARN_ON(!system_supports_fpsimd());
last->st = &current->thread.uw.fpsimd_state;
last->sve_state = current->thread.sve_state;
+ last->za_state = current->thread.za_state;
last->sve_vl = task_get_sve_vl(current);
last->sme_vl = task_get_sme_vl(current);
last->svcr = &current->thread.svcr;
@@ -1500,8 +1505,8 @@ static void fpsimd_bind_task_to_cpu(void)
}

void fpsimd_bind_state_to_cpu(struct user_fpsimd_state *st, void *sve_state,
- unsigned int sve_vl, unsigned int sme_vl,
- u64 *svcr)
+ unsigned int sve_vl, void *za_state,
+ unsigned int sme_vl, u64 *svcr)
{
struct fpsimd_last_state_struct *last =
this_cpu_ptr(&fpsimd_last_state);
@@ -1512,6 +1517,7 @@ void fpsimd_bind_state_to_cpu(struct user_fpsimd_state *st, void *sve_state,
last->st = st;
last->svcr = svcr;
last->sve_state = sve_state;
+ last->za_state = za_state;
last->sve_vl = sve_vl;
last->sme_vl = sme_vl;
}
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 394e583bb73e..57d7ac3cfa0c 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -116,7 +116,7 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
fpsimd_bind_state_to_cpu(&vcpu->arch.ctxt.fp_regs,
vcpu->arch.sve_state,
vcpu->arch.sve_max_vl,
- 0, NULL);
+ NULL, 0, &vcpu->arch.svcr);

clear_thread_flag(TIF_FOREIGN_FPSTATE);
update_thread_flag(TIF_SVE, vcpu_has_sve(vcpu));
--
2.30.2