[PATCH v3 0/2] arm64: Support systems without FP/ASIMD

[PATCH v3 0/2] arm64: Support systems without FP/ASIMD

[Suzuki K Poulose]

This series adds supports to the kernel and KVM hyp to handle
systems without FP/ASIMD properly. At the moment the kernel
doesn't check if the FP unit is available before accessing
the registers (e.g during context switch). Also for KVM,
we trap the FP/ASIMD accesses and handle it by injecting an
undefined instruction into the VM on systems without FP.

Tested on a FVP_Base-AEM-v8A model by disabling VFP on at
least one CPU ( -C clusterX.cpuY.vfp-present=0 ).

Changes since V2:
 - Dropped cleanup patch for arm64/crypto/aes-ce-ccm-glue.c
 - Removed static_key check from cpus_have_cap. All users with
   constant caps should use the new API to make use of static_keys.
 - Removed a dedicated static_key used in irqchip-gic-v3.c for
   Cavium errata with the new API.

Applies on v4.9-rc4 + [1] (which is pushed for rc5)

[1] http://marc.info/?l=linux-arm-kernel&m=147819889813214&w=2


Suzuki K Poulose (2):
  arm64: Add hypervisor safe helper for checking constant capabilities
  arm64: Support systems without FP/ASIMD

 arch/arm64/include/asm/cpucaps.h    |  3 ++-
 arch/arm64/include/asm/cpufeature.h | 24 +++++++++++++++++-------
 arch/arm64/include/asm/neon.h       |  3 ++-
 arch/arm64/kernel/cpufeature.c      | 17 ++++++++++++++++-
 arch/arm64/kernel/fpsimd.c          | 14 ++++++++++++++
 arch/arm64/kernel/process.c         |  2 +-
 arch/arm64/kvm/handle_exit.c        | 11 +++++++++++
 arch/arm64/kvm/hyp/hyp-entry.S      |  9 ++++++++-
 arch/arm64/kvm/hyp/switch.c         |  5 ++++-
 drivers/irqchip/irq-gic-v3.c        | 13 +------------
 10 files changed, 76 insertions(+), 25 deletions(-)

-- 
2.7.4

[PATCH v3 1/2] arm64: Add hypervisor safe helper for checking constant capabilities

[Suzuki K Poulose]

The hypervisor may not have full access to the kernel data structures
and hence cannot safely use cpus_have_cap() helper for checking the
system capability. Add a safe helper for hypervisors to check a constant
system capability, which *doesn't* fall back to checking the bitmap
maintained by the kernel. With this, make the cpus_have_cap() only
check the bitmask and force constant cap checks to use the new API
for quicker checks.

Cc: Robert Ritcher <rritcher@cavium.com>
Cc: Tirumalesh Chalamarla <tchalamarla@cavium.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/include/asm/cpufeature.h | 19 ++++++++++++-------
 arch/arm64/kernel/cpufeature.c      |  2 +-
 arch/arm64/kernel/process.c         |  2 +-
 drivers/irqchip/irq-gic-v3.c        | 13 +------------
 4 files changed, 15 insertions(+), 21 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 0bc0b1d..9890d20 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -9,8 +9,6 @@
 #ifndef __ASM_CPUFEATURE_H
 #define __ASM_CPUFEATURE_H
 
-#include <linux/jump_label.h>
-
 #include <asm/cpucaps.h>
 #include <asm/hwcap.h>
 #include <asm/sysreg.h>
@@ -27,6 +25,8 @@
 
 #ifndef __ASSEMBLY__
 
+#include <linux/bug.h>
+#include <linux/jump_label.h>
 #include <linux/kernel.h>
 
 /* CPU feature register tracking */
@@ -104,14 +104,19 @@ static inline bool cpu_have_feature(unsigned int num)
 	return elf_hwcap & (1UL << num);
 }
 
+/* System capability check for constant caps */
+static inline bool cpus_have_const_cap(int num)
+{
+	if (num >= ARM64_NCAPS)
+		return false;
+	return static_branch_unlikely(&cpu_hwcap_keys[num]);
+}
+
 static inline bool cpus_have_cap(unsigned int num)
 {
 	if (num >= ARM64_NCAPS)
 		return false;
-	if (__builtin_constant_p(num))
-		return static_branch_unlikely(&cpu_hwcap_keys[num]);
-	else
-		return test_bit(num, cpu_hwcaps);
+	return test_bit(num, cpu_hwcaps);
 }
 
 static inline void cpus_set_cap(unsigned int num)
@@ -200,7 +205,7 @@ static inline bool cpu_supports_mixed_endian_el0(void)
 
 static inline bool system_supports_32bit_el0(void)
 {
-	return cpus_have_cap(ARM64_HAS_32BIT_EL0);
+	return cpus_have_const_cap(ARM64_HAS_32BIT_EL0);
 }
 
 static inline bool system_supports_mixed_endian_el0(void)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index c02504e..fc2bd19 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1102,5 +1102,5 @@ void __init setup_cpu_features(void)
 static bool __maybe_unused
 cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
 {
-	return (cpus_have_cap(ARM64_HAS_PAN) && !cpus_have_cap(ARM64_HAS_UAO));
+	return (cpus_have_const_cap(ARM64_HAS_PAN) && !cpus_have_const_cap(ARM64_HAS_UAO));
 }
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 01753cd..18354f3 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -282,7 +282,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->pstate = PSR_MODE_EL1h;
 		if (IS_ENABLED(CONFIG_ARM64_UAO) &&
-		    cpus_have_cap(ARM64_HAS_UAO))
+		    cpus_have_const_cap(ARM64_HAS_UAO))
 			childregs->pstate |= PSR_UAO_BIT;
 		p->thread.cpu_context.x19 = stack_start;
 		p->thread.cpu_context.x20 = stk_sz;
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 19d642e..26e1d7f 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -120,11 +120,10 @@ static void gic_redist_wait_for_rwp(void)
 }
 
 #ifdef CONFIG_ARM64
-static DEFINE_STATIC_KEY_FALSE(is_cavium_thunderx);
 
 static u64 __maybe_unused gic_read_iar(void)
 {
-	if (static_branch_unlikely(&is_cavium_thunderx))
+	if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM_23154))
 		return gic_read_iar_cavium_thunderx();
 	else
 		return gic_read_iar_common();
@@ -905,14 +904,6 @@ static const struct irq_domain_ops partition_domain_ops = {
 	.select = gic_irq_domain_select,
 };
 
-static void gicv3_enable_quirks(void)
-{
-#ifdef CONFIG_ARM64
-	if (cpus_have_cap(ARM64_WORKAROUND_CAVIUM_23154))
-		static_branch_enable(&is_cavium_thunderx);
-#endif
-}
-
 static int __init gic_init_bases(void __iomem *dist_base,
 				 struct redist_region *rdist_regs,
 				 u32 nr_redist_regions,
@@ -935,8 +926,6 @@ static int __init gic_init_bases(void __iomem *dist_base,
 	gic_data.nr_redist_regions = nr_redist_regions;
 	gic_data.redist_stride = redist_stride;
 
-	gicv3_enable_quirks();
-
 	/*
 	 * Find out how many interrupts are supported.
 	 * The GIC only supports up to 1020 interrupt sources (SGI+PPI+SPI)
-- 
2.7.4

[PATCH v3 2/2] arm64: Support systems without FP/ASIMD

[Suzuki K Poulose]

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_partial() 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/include/asm/cpucaps.h    |  3 ++-
 arch/arm64/include/asm/cpufeature.h |  5 +++++
 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 ++++-
 8 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 87b4465..4174f09 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -34,7 +34,8 @@
 #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
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9890d20..ce45770 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -213,6 +213,11 @@ 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 fc2bd19..f89385d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -746,6 +746,14 @@ 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",
@@ -829,6 +837,13 @@ 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 394c61d..b883f1f 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 a204adf..1bfe30d 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 4e92399..5e9052f 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -106,9 +106,16 @@ el1_trap:
 	 * x0: 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	x0, #ESR_ELx_EC_FP_ASIMD
 	b.eq	__fpsimd_guest_restore
+alternative_else_nop_endif
 
 	mrs	x1, tpidr_el2
 	mov	x0, #ARM_EXCEPTION_TRAP
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 83037cd..8bcae7b 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -21,6 +21,7 @@
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_hyp.h>
+#include <asm/fpsimd.h>
 
 static bool __hyp_text __fpsimd_enabled_nvhe(void)
 {
@@ -76,9 +77,11 @@ 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

Re: [PATCH v3 1/2] arm64: Add hypervisor safe helper for checking constant capabilities

[Will Deacon]

On Tue, Nov 08, 2016 at 01:56:20PM +0000, Suzuki K Poulose wrote:
> The hypervisor may not have full access to the kernel data structures
> and hence cannot safely use cpus_have_cap() helper for checking the
> system capability. Add a safe helper for hypervisors to check a constant
> system capability, which *doesn't* fall back to checking the bitmap
> maintained by the kernel. With this, make the cpus_have_cap() only
> check the bitmask and force constant cap checks to use the new API
> for quicker checks.
> 
> Cc: Robert Ritcher <rritcher@cavium.com>
> Cc: Tirumalesh Chalamarla <tchalamarla@cavium.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>  arch/arm64/include/asm/cpufeature.h | 19 ++++++++++++-------
>  arch/arm64/kernel/cpufeature.c      |  2 +-
>  arch/arm64/kernel/process.c         |  2 +-
>  drivers/irqchip/irq-gic-v3.c        | 13 +------------

It might be worth having the GIC changes as a separate patch, but either
way:

Reviewed-by: Will Deacon <will.deacon@arm.com>

Will

Re: [PATCH v3 0/2] arm64: Support systems without FP/ASIMD

[Marc Zyngier]

On 08/11/16 13:56, Suzuki K Poulose wrote:
> This series adds supports to the kernel and KVM hyp to handle
> systems without FP/ASIMD properly. At the moment the kernel
> doesn't check if the FP unit is available before accessing
> the registers (e.g during context switch). Also for KVM,
> we trap the FP/ASIMD accesses and handle it by injecting an
> undefined instruction into the VM on systems without FP.
> 
> Tested on a FVP_Base-AEM-v8A model by disabling VFP on at
> least one CPU ( -C clusterX.cpuY.vfp-present=0 ).
> 
> Changes since V2:
>  - Dropped cleanup patch for arm64/crypto/aes-ce-ccm-glue.c
>  - Removed static_key check from cpus_have_cap. All users with
>    constant caps should use the new API to make use of static_keys.
>  - Removed a dedicated static_key used in irqchip-gic-v3.c for
>    Cavium errata with the new API.
> 
> Applies on v4.9-rc4 + [1] (which is pushed for rc5)
> 
> [1] http://marc.info/?l=linux-arm-kernel&m=147819889813214&w=2
> 
> 
> Suzuki K Poulose (2):
>   arm64: Add hypervisor safe helper for checking constant capabilities
>   arm64: Support systems without FP/ASIMD
> 
>  arch/arm64/include/asm/cpucaps.h    |  3 ++-
>  arch/arm64/include/asm/cpufeature.h | 24 +++++++++++++++++-------
>  arch/arm64/include/asm/neon.h       |  3 ++-
>  arch/arm64/kernel/cpufeature.c      | 17 ++++++++++++++++-
>  arch/arm64/kernel/fpsimd.c          | 14 ++++++++++++++
>  arch/arm64/kernel/process.c         |  2 +-
>  arch/arm64/kvm/handle_exit.c        | 11 +++++++++++
>  arch/arm64/kvm/hyp/hyp-entry.S      |  9 ++++++++-
>  arch/arm64/kvm/hyp/switch.c         |  5 ++++-
>  drivers/irqchip/irq-gic-v3.c        | 13 +------------
>  10 files changed, 76 insertions(+), 25 deletions(-)
> 

For the series:

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>

How do we plan on merging this? Catalin, are you willing to take it all?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

Re: [PATCH v3 0/2] arm64: Support systems without FP/ASIMD

[Catalin Marinas]

On Fri, Nov 11, 2016 at 01:41:37PM +0000, Marc Zyngier wrote:
> On 08/11/16 13:56, Suzuki K Poulose wrote:
> > This series adds supports to the kernel and KVM hyp to handle
> > systems without FP/ASIMD properly. At the moment the kernel
> > doesn't check if the FP unit is available before accessing
> > the registers (e.g during context switch). Also for KVM,
> > we trap the FP/ASIMD accesses and handle it by injecting an
> > undefined instruction into the VM on systems without FP.
> > 
> > Tested on a FVP_Base-AEM-v8A model by disabling VFP on at
> > least one CPU ( -C clusterX.cpuY.vfp-present=0 ).
> > 
> > Changes since V2:
> >  - Dropped cleanup patch for arm64/crypto/aes-ce-ccm-glue.c
> >  - Removed static_key check from cpus_have_cap. All users with
> >    constant caps should use the new API to make use of static_keys.
> >  - Removed a dedicated static_key used in irqchip-gic-v3.c for
> >    Cavium errata with the new API.
> > 
> > Applies on v4.9-rc4 + [1] (which is pushed for rc5)
> > 
> > [1] http://marc.info/?l=linux-arm-kernel&m=147819889813214&w=2
> > 
> > 
> > Suzuki K Poulose (2):
> >   arm64: Add hypervisor safe helper for checking constant capabilities
> >   arm64: Support systems without FP/ASIMD
> > 
> >  arch/arm64/include/asm/cpucaps.h    |  3 ++-
> >  arch/arm64/include/asm/cpufeature.h | 24 +++++++++++++++++-------
> >  arch/arm64/include/asm/neon.h       |  3 ++-
> >  arch/arm64/kernel/cpufeature.c      | 17 ++++++++++++++++-
> >  arch/arm64/kernel/fpsimd.c          | 14 ++++++++++++++
> >  arch/arm64/kernel/process.c         |  2 +-
> >  arch/arm64/kvm/handle_exit.c        | 11 +++++++++++
> >  arch/arm64/kvm/hyp/hyp-entry.S      |  9 ++++++++-
> >  arch/arm64/kvm/hyp/switch.c         |  5 ++++-
> >  drivers/irqchip/irq-gic-v3.c        | 13 +------------
> >  10 files changed, 76 insertions(+), 25 deletions(-)
> 
> For the series:
> 
> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
> 
> How do we plan on merging this? Catalin, are you willing to take it all?

Happy to take it all through the arm64 tree. Thanks for the review.

-- 
Catalin

Re: [PATCH v3 2/2] arm64: Support systems without FP/ASIMD

[Catalin Marinas]

Hi Suzuki,

On Tue, Nov 08, 2016 at 01:56:21PM +0000, Suzuki K. Poulose wrote:
> diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
> index 87b4465..4174f09 100644
> --- a/arch/arm64/include/asm/cpucaps.h
> +++ b/arch/arm64/include/asm/cpucaps.h
> @@ -34,7 +34,8 @@
>  #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
>  
>  #endif /* __ASM_CPUCAPS_H */
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 9890d20..ce45770 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -213,6 +213,11 @@ 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);
> +}

Any particular reason why using negation instead of a ARM64_HAS_FPSIMD?
A potential problem would be the default cpus_have_const_cap()
implementation and the default static key having a slight performance
impact.

> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index fc2bd19..f89385d 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -746,6 +746,14 @@ 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",
> @@ -829,6 +837,13 @@ 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,
> +	},

If we go for negation, I don't think we need a min_field_value at all,
the matching is done by the has_no_fpsimd() function.

-- 
Catalin

Re: [PATCH v3 2/2] arm64: Support systems without FP/ASIMD

[Suzuki K Poulose]

On 14/11/16 11:48, Catalin Marinas wrote:
> Hi Suzuki,
>

>> +static inline bool system_supports_fpsimd(void)
>> +{
>> +	return !cpus_have_const_cap(ARM64_HAS_NO_FPSIMD);
>> +}
>
> Any particular reason why using negation instead of a ARM64_HAS_FPSIMD?
> A potential problem would be the default cpus_have_const_cap()
> implementation and the default static key having a slight performance
> impact.

The negation was chosen to avoid hotpatching in the most common case.
But as you said, it has an impact on the other side. I think doing
a one time hotpatching at boot time is more optimal than penalising
a bunch of other users throughout the execution. I will take a look
at changing it back to a ARM64_HAS_FPSIMD.

>>  	},
>> +	{
>> +		/* FP/SIMD is not implemented */
>> +		.capability = ARM64_HAS_NO_FPSIMD,
>> +		.def_scope = SCOPE_SYSTEM,
>> +		.min_field_value = 0,
>> +		.matches = has_no_fpsimd,
>> +	},
>
> If we go for negation, I don't think we need a min_field_value at all,
> the matching is done by the has_no_fpsimd() function.

You're right.

Suzuki

Re: [PATCH v3 0/2] arm64: Support systems without FP/ASIMD

[Catalin Marinas]

On Tue, Nov 08, 2016 at 01:56:19PM +0000, Suzuki K. Poulose wrote:
> This series adds supports to the kernel and KVM hyp to handle
> systems without FP/ASIMD properly. At the moment the kernel
> doesn't check if the FP unit is available before accessing
> the registers (e.g during context switch). Also for KVM,
> we trap the FP/ASIMD accesses and handle it by injecting an
> undefined instruction into the VM on systems without FP.
> 
> Tested on a FVP_Base-AEM-v8A model by disabling VFP on at
> least one CPU ( -C clusterX.cpuY.vfp-present=0 ).
> 
> Changes since V2:
>  - Dropped cleanup patch for arm64/crypto/aes-ce-ccm-glue.c
>  - Removed static_key check from cpus_have_cap. All users with
>    constant caps should use the new API to make use of static_keys.
>  - Removed a dedicated static_key used in irqchip-gic-v3.c for
>    Cavium errata with the new API.
> 
> Applies on v4.9-rc4 + [1] (which is pushed for rc5)
> 
> [1] http://marc.info/?l=linux-arm-kernel&m=147819889813214&w=2

I queued the patches for 4.10 with a slight modification as I haven't
cherry-picked the patch above. I'll push the for-next/core branch out
once I've done some testing.

Thanks.

-- 
Catalin