[PATCH v2] arm64: context: Fix ASID limit in boot warning

[PATCH v2] arm64: context: Fix ASID limit in boot warning

[Jean-Philippe Brucker]

Since commit f88f42f853a8 ("arm64: context: Free up kernel ASIDs if KPTI
is not in use"), the NUM_USER_ASIDS macro doesn't correspond to the
effective number of ASIDs when KPTI is enabled. Get an accurate number
of available ASIDs in an arch_initcall, once we've discovered all CPUs'
capabilities and know if we still need to halve the ASID space for KPTI.

Fixes: f88f42f853a8 ("arm64: context: Free up kernel ASIDs if KPTI is not in use")
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
v1->v2: move warning to arch_initcall(), post capabilities (e.g. E0PD)
        discovery

This change may be a little invasive for just a validation warning, but
it will likely be needed later, in the asid-pinning patch I'd like to
introduce for IOMMU SVA.
---
 arch/arm64/mm/context.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index 8ef73e89d514..efe98f0dcc89 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -260,14 +260,23 @@ asmlinkage void post_ttbr_update_workaround(void)
 			CONFIG_CAVIUM_ERRATUM_27456));
 }
 
-static int asids_init(void)
+static int asids_update_limit(void)
 {
-	asid_bits = get_cpu_asid_bits();
 	/*
 	 * Expect allocation after rollover to fail if we don't have at least
 	 * one more ASID than CPUs. ASID #0 is reserved for init_mm.
 	 */
-	WARN_ON(NUM_USER_ASIDS - 1 <= num_possible_cpus());
+	bool kpti = arm64_kernel_unmapped_at_el0();
+	unsigned long num_available_asids = (1UL << (asid_bits - kpti)) - 1;
+
+	WARN_ON(num_available_asids <= num_possible_cpus());
+	return 0;
+}
+arch_initcall(asids_update_limit);
+
+static int asids_init(void)
+{
+	asid_bits = get_cpu_asid_bits();
 	atomic64_set(&asid_generation, ASID_FIRST_VERSION);
 	asid_map = kcalloc(BITS_TO_LONGS(NUM_USER_ASIDS), sizeof(*asid_map),
 			   GFP_KERNEL);
-- 
2.25.0


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Re: [PATCH v2] arm64: context: Fix ASID limit in boot warning

[Vladimir Murzin]

On 2/26/20 12:37 PM, Jean-Philippe Brucker wrote:
> Since commit f88f42f853a8 ("arm64: context: Free up kernel ASIDs if KPTI
> is not in use"), the NUM_USER_ASIDS macro doesn't correspond to the
> effective number of ASIDs when KPTI is enabled. Get an accurate number
> of available ASIDs in an arch_initcall, once we've discovered all CPUs'
> capabilities and know if we still need to halve the ASID space for KPTI.
> 
> Fixes: f88f42f853a8 ("arm64: context: Free up kernel ASIDs if KPTI is not in use")
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
> v1->v2: move warning to arch_initcall(), post capabilities (e.g. E0PD)
>         discovery
> 
> This change may be a little invasive for just a validation warning, but
> it will likely be needed later, in the asid-pinning patch I'd like to
> introduce for IOMMU SVA.
> ---
>  arch/arm64/mm/context.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
> index 8ef73e89d514..efe98f0dcc89 100644
> --- a/arch/arm64/mm/context.c
> +++ b/arch/arm64/mm/context.c
> @@ -260,14 +260,23 @@ asmlinkage void post_ttbr_update_workaround(void)
>  			CONFIG_CAVIUM_ERRATUM_27456));
>  }
>  
> -static int asids_init(void)
> +static int asids_update_limit(void)
>  {
> -	asid_bits = get_cpu_asid_bits();
>  	/*
>  	 * Expect allocation after rollover to fail if we don't have at least
>  	 * one more ASID than CPUs. ASID #0 is reserved for init_mm.
>  	 */
> -	WARN_ON(NUM_USER_ASIDS - 1 <= num_possible_cpus());
> +	bool kpti = arm64_kernel_unmapped_at_el0();
> +	unsigned long num_available_asids = (1UL << (asid_bits - kpti)) - 1;
> +
> +	WARN_ON(num_available_asids <= num_possible_cpus());
> +	return 0;
> +}

Since we have actual number of ASIDs here can we move pr_info here as well? No
need to re-spin immediately.

Cheers
Vladimir

> +arch_initcall(asids_update_limit);
> +
> +static int asids_init(void)
> +{
> +	asid_bits = get_cpu_asid_bits();
>  	atomic64_set(&asid_generation, ASID_FIRST_VERSION);
>  	asid_map = kcalloc(BITS_TO_LONGS(NUM_USER_ASIDS), sizeof(*asid_map),
>  			   GFP_KERNEL);
> 


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Re: [PATCH v2] arm64: context: Fix ASID limit in boot warning

[Robin Murphy]

On 26/02/2020 12:37 pm, Jean-Philippe Brucker wrote:
> Since commit f88f42f853a8 ("arm64: context: Free up kernel ASIDs if KPTI
> is not in use"), the NUM_USER_ASIDS macro doesn't correspond to the
> effective number of ASIDs when KPTI is enabled. Get an accurate number
> of available ASIDs in an arch_initcall, once we've discovered all CPUs'
> capabilities and know if we still need to halve the ASID space for KPTI.
> 
> Fixes: f88f42f853a8 ("arm64: context: Free up kernel ASIDs if KPTI is not in use")
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
> v1->v2: move warning to arch_initcall(), post capabilities (e.g. E0PD)
>          discovery
> 
> This change may be a little invasive for just a validation warning, but
> it will likely be needed later, in the asid-pinning patch I'd like to
> introduce for IOMMU SVA.
> ---
>   arch/arm64/mm/context.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
> index 8ef73e89d514..efe98f0dcc89 100644
> --- a/arch/arm64/mm/context.c
> +++ b/arch/arm64/mm/context.c
> @@ -260,14 +260,23 @@ asmlinkage void post_ttbr_update_workaround(void)
>   			CONFIG_CAVIUM_ERRATUM_27456));
>   }
>   
> -static int asids_init(void)
> +static int asids_update_limit(void)
>   {
> -	asid_bits = get_cpu_asid_bits();
>   	/*
>   	 * Expect allocation after rollover to fail if we don't have at least
>   	 * one more ASID than CPUs. ASID #0 is reserved for init_mm.
>   	 */
> -	WARN_ON(NUM_USER_ASIDS - 1 <= num_possible_cpus());
> +	bool kpti = arm64_kernel_unmapped_at_el0();
> +	unsigned long num_available_asids = (1UL << (asid_bits - kpti)) - 1;

Yikes! Could the adjustment be a little more obvious please? e.g.:

	if (arm64_kernel_unmapped_at_el0())
		num_available_asids /= 2;

I assume this isn't a path where we need to shave off every last cycle 
possible.

Robin.

> +
> +	WARN_ON(num_available_asids <= num_possible_cpus());
> +	return 0;
> +}
> +arch_initcall(asids_update_limit);
> +
> +static int asids_init(void)
> +{
> +	asid_bits = get_cpu_asid_bits();
>   	atomic64_set(&asid_generation, ASID_FIRST_VERSION);
>   	asid_map = kcalloc(BITS_TO_LONGS(NUM_USER_ASIDS), sizeof(*asid_map),
>   			   GFP_KERNEL);
> 

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