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SubjectRe: [PATCH v2 2/2] irqchip/gic-v3: Support pseudo-NMIs when SCR_EL3.FIQ == 0
Hi Alex,

Thanks for taking the time for putting this together, as it has been a
long standing issue that needed fixing.

On Wed, 19 Aug 2020 14:36:30 +0100,
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
>
> The GIC's internal view of the priority mask register and the assigned
> interrupt priorities are based on whether GIC security is enabled and
> whether firmware routes Group 0 interrupts to EL3. At the moment, we
> support priority masking when ICC_PMR_EL1 and interrupt priorities are
> either both modified by the GIC, or both left unchanged.
>
> Trusted Firmware-A's default interrupt routing model allows Group 0
> interrupts to be delivered to the non-secure world (SCR_EL3.FIQ == 0).
> Unfortunately, this is precisely the case that the GIC driver doesn't
> support: ICC_PMR_EL1 remains unchanged, but the GIC's view of interrupt
> priorities is different from the software programmed values.
>
> Support pseudo-NMIs when SCR_EL3.FIQ == 0 by using a different value to
> mask regular interrupts. All the other values remain the same.
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
> arch/arm64/include/asm/arch_gicv3.h | 8 ++++-
> arch/arm64/include/asm/daifflags.h | 4 +--
> arch/arm64/include/asm/irqflags.h | 18 ++++++----
> arch/arm64/include/asm/ptrace.h | 12 +++++++
> arch/arm64/kernel/entry.S | 2 +-
> arch/arm64/kernel/image-vars.h | 2 ++
> arch/arm64/kvm/hyp/nvhe/switch.c | 2 +-
> drivers/irqchip/irq-gic-v3.c | 52 ++++++++++++++++++++++-------
> 8 files changed, 77 insertions(+), 23 deletions(-)
>
> diff --git a/arch/arm64/include/asm/arch_gicv3.h b/arch/arm64/include/asm/arch_gicv3.h
> index 6647ae4f0231..908152e8659b 100644
> --- a/arch/arm64/include/asm/arch_gicv3.h
> +++ b/arch/arm64/include/asm/arch_gicv3.h
> @@ -162,7 +162,13 @@ static inline void gic_pmr_mask_irqs(void)
> * are applied to IRQ priorities
> */
> BUILD_BUG_ON((0x80 | (GICD_INT_DEF_PRI >> 1)) >= GIC_PRIO_IRQON);
> - gic_write_pmr(GIC_PRIO_IRQOFF);
> + /*
> + * Same situation as above, but now we make sure that we can mask
> + * regular interrupts.
> + */
> + BUILD_BUG_ON((0x80 | (GICD_INT_DEF_PRI >> 1)) < (GIC_PRIO_IRQOFF_NS |
> + GIC_PRIO_PSR_I_SET));
> + gic_write_pmr(gic_prio_irqoff());
> }
>
> static inline void gic_arch_enable_irqs(void)
> diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
> index ec213b4a1650..3efa240a6c48 100644
> --- a/arch/arm64/include/asm/daifflags.h
> +++ b/arch/arm64/include/asm/daifflags.h
> @@ -22,7 +22,7 @@
> static inline void local_daif_mask(void)
> {
> WARN_ON(system_has_prio_mask_debugging() &&
> - (read_sysreg_s(SYS_ICC_PMR_EL1) == (GIC_PRIO_IRQOFF |
> + (read_sysreg_s(SYS_ICC_PMR_EL1) == (gic_prio_irqoff() |
> GIC_PRIO_PSR_I_SET)));
>
> asm volatile(
> @@ -87,7 +87,7 @@ static inline void local_daif_restore(unsigned long flags)
> * asynchronous errors, we can take NMIs
> */
> flags &= ~PSR_I_BIT;
> - pmr = GIC_PRIO_IRQOFF;
> + pmr = gic_prio_irqoff();
> } else {
> pmr = GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET;
> }
> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index aa4b6521ef14..af353c78d5f8 100644
> --- a/arch/arm64/include/asm/irqflags.h
> +++ b/arch/arm64/include/asm/irqflags.h
> @@ -28,10 +28,13 @@
> */
> static inline void arch_local_irq_enable(void)
> {
> + u64 pmr_irqon = GIC_PRIO_IRQON;
> +
> if (system_has_prio_mask_debugging()) {
> - u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
> + u64 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
> + u64 pmr_irqoff = gic_prio_irqoff();
>
> - WARN_ON_ONCE(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
> + WARN_ON_ONCE(pmr != pmr_irqon && pmr != pmr_irqoff);
> }
>
> asm volatile(ALTERNATIVE(
> @@ -39,7 +42,7 @@ static inline void arch_local_irq_enable(void)
> __msr_s(SYS_ICC_PMR_EL1, "%0"),
> ARM64_HAS_IRQ_PRIO_MASKING)
> :
> - : "r" ((unsigned long) GIC_PRIO_IRQON)
> + : "r" (pmr_irqon)
> : "memory");
>
> pmr_sync();
> @@ -47,10 +50,13 @@ static inline void arch_local_irq_enable(void)
>
> static inline void arch_local_irq_disable(void)
> {
> + u64 pmr_irqoff = gic_prio_irqoff();
> +
> if (system_has_prio_mask_debugging()) {
> - u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
> + u64 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
> + u64 pmr_irqon = GIC_PRIO_IRQON;
>
> - WARN_ON_ONCE(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
> + WARN_ON_ONCE(pmr != pmr_irqon && pmr != pmr_irqoff);
> }
>
> asm volatile(ALTERNATIVE(
> @@ -58,7 +64,7 @@ static inline void arch_local_irq_disable(void)
> __msr_s(SYS_ICC_PMR_EL1, "%0"),
> ARM64_HAS_IRQ_PRIO_MASKING)
> :
> - : "r" ((unsigned long) GIC_PRIO_IRQOFF)
> + : "r" (pmr_irqoff)
> : "memory");
> }

I believe all the changes in this file can be avoided, see below.

>
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index 966ed30ed5f7..a19cd6ff4d1b 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -32,6 +32,7 @@
> */
> #define GIC_PRIO_IRQON 0xe0
> #define GIC_PRIO_IRQOFF (GIC_PRIO_IRQON & ~0x80)
> +#define GIC_PRIO_IRQOFF_NS 0xa0
> #define GIC_PRIO_PSR_I_SET (1 << 4)
>
> /* Additional SPSR bits not exposed in the UABI */
> @@ -129,6 +130,17 @@
> #define compat_sp_fiq regs[29]
> #define compat_lr_fiq regs[30]
>
> +#define gic_prio_irqoff() \
> + ({ \
> + extern struct static_key_false gic_nonsecure_priorities;\
> + u8 __prio = GIC_PRIO_IRQOFF; \
> + \
> + if (static_branch_unlikely(&gic_nonsecure_priorities)) \
> + __prio = GIC_PRIO_IRQOFF_NS; \
> + \
> + __prio; \
> + })
> +

This single change is causing quite a lot of churn, most of which
could be avoided if you actually reused the macro name:

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 966ed30ed5f7..f85a00817fa5 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -31,9 +31,21 @@
* interrupt disabling temporarily does not rely on IRQ priorities.
*/
#define GIC_PRIO_IRQON 0xe0
-#define GIC_PRIO_IRQOFF (GIC_PRIO_IRQON & ~0x80)
+#define __GIC_PRIO_IRQOFF (GIC_PRIO_IRQON & ~0x80)
+#define __GIC_PRIO_IRQOFF_NS 0xa0
#define GIC_PRIO_PSR_I_SET (1 << 4)

+#define GIC_PRIO_IRQOFF \
+ ({ \
+ extern struct static_key_false gic_nonsecure_priorities;\
+ u8 __prio = __GIC_PRIO_IRQOFF; \
+ \
+ if (static_branch_unlikely(&gic_nonsecure_priorities)) \
+ __prio = __GIC_PRIO_IRQOFF_NS; \
+ \
+ __prio; \
+ })
+
/* Additional SPSR bits not exposed in the UABI */
#define PSR_MODE_THREAD_BIT (1 << 0)
#define PSR_IL_BIT (1 << 20)
"With this simple trick", a lot of the churn in this patch vanishes:

arch/arm64/include/asm/arch_gicv3.h | 8 +++++-
arch/arm64/include/asm/ptrace.h | 14 +++++++++-
arch/arm64/kernel/entry.S | 2 +-
arch/arm64/kernel/image-vars.h | 2 ++
drivers/irqchip/irq-gic-v3.c | 52 ++++++++++++++++++++++++++++---------
5 files changed, 63 insertions(+), 15 deletions(-)
> static inline unsigned long compat_psr_to_pstate(const unsigned long psr)
> {
> unsigned long pstate;
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 2646178c8329..e4fa944dbf1d 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -653,7 +653,7 @@ alternative_else_nop_endif
> #ifdef CONFIG_ARM64_PSEUDO_NMI
> /*
> * When using IRQ priority masking, we can get spurious interrupts while
> - * PMR is set to GIC_PRIO_IRQOFF. An NMI might also have occurred in a
> + * PMR is set to mask interrupts. An NMI might also have occurred in a
> * section with interrupts disabled. Skip tracing in those cases.
> */
> test_irqs_unmasked res=x0, pmr=x20
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index 9e897c500237..c4476a99dee8 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -101,6 +101,8 @@ KVM_NVHE_ALIAS(vgic_v3_cpuif_trap);
> /* Static key checked in pmr_sync(). */
> #ifdef CONFIG_ARM64_PSEUDO_NMI
> KVM_NVHE_ALIAS(gic_pmr_sync);
> +/* Static key checked in gic_prio_irqoff(). */
> +KVM_NVHE_ALIAS(gic_nonsecure_priorities);
> #endif
>
> #endif /* CONFIG_KVM */
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index 341be2f2f312..729a3a59ad6a 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -237,7 +237,7 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>
> /* Returning to host will clear PSR.I, remask PMR if needed */
> if (system_uses_irq_prio_masking())
> - gic_write_pmr(GIC_PRIO_IRQOFF);
> + gic_write_pmr(gic_prio_irqoff());
>
> return exit_code;
> }
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index ce8944ae1b84..19e52c025c59 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -75,16 +75,14 @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
> *
> * If SCR_EL3.FIQ == 1, the values writen to/read from PMR and RPR at non-secure
> * EL1 are subject to a similar operation thus matching the priorities presented
> - * from the (re)distributor when security is enabled.
> + * from the (re)distributor when security is enabled. When SCR_EL3.FIQ == 0,
> + * these values are unchanched by the GIC.
> *
> * see GICv3/GICv4 Architecture Specification (IHI0069D):
> * - section 4.8.1 Non-secure accesses to register fields for Secure interrupt
> * priorities.
> * - Figure 4-7 Secure read of the priority field for a Non-secure Group 1
> * interrupt.
> - *
> - * For now, we only support pseudo-NMIs if we have non-secure view of
> - * priorities.
> */
> static DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
>
> @@ -97,6 +95,9 @@ static DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
> DEFINE_STATIC_KEY_FALSE(gic_pmr_sync);
> EXPORT_SYMBOL(gic_pmr_sync);
>
> +DEFINE_STATIC_KEY_FALSE(gic_nonsecure_priorities);
> +EXPORT_SYMBOL(gic_nonsecure_priorities);
> +
> /* ppi_nmi_refs[n] == number of cpus having ppi[n + 16] set as NMI */
> static refcount_t *ppi_nmi_refs;
>
> @@ -932,14 +933,16 @@ static void gic_cpu_sys_reg_init(void)
> /* Set priority mask register */
> if (!gic_prio_masking_enabled()) {
> write_gicreg(DEFAULT_PMR_VALUE, ICC_PMR_EL1);
> - } else {
> + } else if (gic_supports_nmi()) {
> /*
> * Mismatch configuration with boot CPU, the system is likely
> * to die as interrupt masking will not work properly on all
> * CPUs
> */
> - WARN_ON(gic_supports_nmi() && group0 &&
> - !gic_dist_security_disabled());
> + if (static_branch_unlikely(&gic_nonsecure_priorities))
> + WARN_ON(!group0 || gic_dist_security_disabled());
> + else
> + WARN_ON(group0 && !gic_dist_security_disabled());

It'd be worth adding a comment saying that this never runs on the boot
CPU (I just spent 10 minutes wondering why this worked).

> }
>
> /*
> @@ -1544,11 +1547,6 @@ static void gic_enable_nmi_support(void)
> if (!gic_prio_masking_enabled())
> return;
>
> - if (gic_has_group0() && !gic_dist_security_disabled()) {
> - pr_warn("SCR_EL3.FIQ is cleared, cannot enable use of pseudo-NMIs\n");
> - return;
> - }
> -
> ppi_nmi_refs = kcalloc(gic_data.ppi_nr, sizeof(*ppi_nmi_refs), GFP_KERNEL);
> if (!ppi_nmi_refs)
> return;
> @@ -1567,6 +1565,36 @@ static void gic_enable_nmi_support(void)
> pr_info("Pseudo-NMIs enabled using %s ICC_PMR_EL1 synchronisation\n",
> static_branch_unlikely(&gic_pmr_sync) ? "forced" : "relaxed");
>
> + /*
> + * How priority values are used by the GIC depends on two things:
> + * the security state of the GIC (controlled by the GICD_CTRL.DS bit)
> + * and if Group 0 interrupts can be delivered to Linux in the non-secure
> + * world as FIQs (controlled by the SCR_EL3.FIQ bit). These affect the
> + * the ICC_PMR_EL1 register and the priority that software assigns to
> + * interrupts:
> + *
> + * GICD_CTRL.DS | SCR_EL3.FIQ | ICC_PMR_EL1 | Group 1 priority
> + * -----------------------------------------------------------
> + * 1 | - | unchanged | unchanged
> + * -----------------------------------------------------------
> + * 0 | 1 | non-secure | non-secure
> + * -----------------------------------------------------------
> + * 0 | 0 | unchanged | non-secure
> + *
> + * where non-secure means that the value is right-shifted by one and the
> + * MSB bit set, to make it fit in the non-secure priority range.
> + *
> + * In the first two cases, where ICC_PMR_EL1 and the interrupt priority
> + * are both either modified, or unchanged, we can use the same set of
> + * priorities.
> + *
> + * In the last case, where only the interrupt priorities are modified to
> + * be in the non-secure range, we use a different PMR value to mask IRQs
> + * and the rest of the values that we use remain unchanged.
> + */
> + if (gic_has_group0() && !gic_dist_security_disabled())
> + static_branch_enable(&gic_nonsecure_priorities);
> +
> static_branch_enable(&supports_pseudo_nmis);
>
> if (static_branch_likely(&supports_deactivate_key))
> --
> 2.28.0
>
>

Otherwise, this looks pretty good, and I'd like to take this into 5.10
if you can respin it quickly.

Thanks,

M.

--
Without deviation from the norm, progress is not possible.

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