Re: [kvm-unit-tests PATCH 2/2] arm64: Check if the configured translation granule is supported

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi,

On 11/3/20 10:02 AM, Andrew Jones wrote:
> On Mon, Nov 02, 2020 at 11:34:44AM +0000, Nikos Nikoleris wrote:
>> Now that we can change the translation granule at will, and since
>> arm64 implementations can support a subset of the architecturally
>> defined granules, we need to check and warn the user if the configured
>> granule is not supported.
> nit: it'd be better for this patch to come before the last patch.
>
>> Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
>> ---
>>  lib/arm64/asm/processor.h | 65 +++++++++++++++++++++++++++++++++++++++
>>  lib/arm/mmu.c             |  3 ++
>>  2 files changed, 68 insertions(+)
>>
>> diff --git a/lib/arm64/asm/processor.h b/lib/arm64/asm/processor.h
>> index 02665b8..0eac928 100644
>> --- a/lib/arm64/asm/processor.h
>> +++ b/lib/arm64/asm/processor.h
>> @@ -117,5 +117,70 @@ static inline u64 get_ctr(void)
>>  
>>  extern u32 dcache_line_size;
>>  
>> +static inline unsigned long get_id_aa64mmfr0_el1(void)
>> +{
>> +	unsigned long mmfr0;
>> +	asm volatile("mrs %0, id_aa64mmfr0_el1" : "=r" (mmfr0));
>> +	return mmfr0;
>> +}
>> +
>> +/* From arch/arm64/include/asm/cpufeature.h */
>> +static inline unsigned int
>> +cpuid_feature_extract_unsigned_field_width(u64 features, int field, int width)
>> +{
>> +	return (u64)(features << (64 - width - field)) >> (64 - width);
>> +}
>> +
>> +#define ID_AA64MMFR0_TGRAN4_SHIFT	28
>> +#define ID_AA64MMFR0_TGRAN64_SHIFT	24
>> +#define ID_AA64MMFR0_TGRAN16_SHIFT	20
>> +#define ID_AA64MMFR0_TGRAN4_SUPPORTED	0x0
>> +#define ID_AA64MMFR0_TGRAN64_SUPPORTED	0x0
>> +#define ID_AA64MMFR0_TGRAN16_SUPPORTED	0x1
>> +
>> +static inline bool system_supports_64kb_granule(void)
>> +{
>> +	u64 mmfr0;
>> +	u32 val;
>> +
>> +	mmfr0 = get_id_aa64mmfr0_el1();
>> +	val = cpuid_feature_extract_unsigned_field_width(
>> +		mmfr0, ID_AA64MMFR0_TGRAN4_SHIFT,4);
>> +
>> +	return val == ID_AA64MMFR0_TGRAN64_SUPPORTED;
>> +}
>> +
>> +static inline bool system_supports_16kb_granule(void)
>> +{
>> +	u64 mmfr0;
>> +	u32 val;
>> +
>> +	mmfr0 = get_id_aa64mmfr0_el1();
>> +	val = cpuid_feature_extract_unsigned_field_width(
>> +		mmfr0, ID_AA64MMFR0_TGRAN16_SHIFT, 4);
>> +
>> +	return val == ID_AA64MMFR0_TGRAN16_SUPPORTED;
>> +}
>> +
>> +static inline bool system_supports_4kb_granule(void)
>> +{
>> +	u64 mmfr0;
>> +	u32 val;
>> +
>> +	mmfr0 = get_id_aa64mmfr0_el1();
>> +	val = cpuid_feature_extract_unsigned_field_width(
>> +		mmfr0, ID_AA64MMFR0_TGRAN4_SHIFT, 4);
>> +
>> +	return val == ID_AA64MMFR0_TGRAN4_SUPPORTED;
>> +}
>> +
>> +#if PAGE_SIZE == 65536
>> +#define system_supports_configured_granule system_supports_64kb_granule
>> +#elif PAGE_SIZE == 16384
>> +#define system_supports_configured_granule system_supports_16kb_granule
>> +#elif PAGE_SIZE == 4096
>> +#define system_supports_configured_granule system_supports_4kb_granule
>> +#endif
>> +
>>  #endif /* !__ASSEMBLY__ */
>>  #endif /* _ASMARM64_PROCESSOR_H_ */
>> diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c
>> index 6d1c75b..51fa745 100644
>> --- a/lib/arm/mmu.c
>> +++ b/lib/arm/mmu.c
>> @@ -163,6 +163,9 @@ void *setup_mmu(phys_addr_t phys_end)
>>  
>>  #ifdef __aarch64__
>>  	init_alloc_vpage((void*)(4ul << 30));
>> +
>> +	assert_msg(system_supports_configured_granule(),
>> +		   "Unsupported translation granule %d\n", PAGE_SIZE);
>                                                      ^
>                                               needs '%ld' to compile
>>  #endif
>>  
>>  	mmu_idmap = alloc_page();
>> -- 
>> 2.17.1
>>
> I don't think we need the three separate functions. How about just
> doing the following diff?
>
> Thanks,
> drew
>
>
> diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c
> index 540a1e842d5b..fef62f5a9866 100644
> --- a/lib/arm/mmu.c
> +++ b/lib/arm/mmu.c
> @@ -160,6 +160,9 @@ void *setup_mmu(phys_addr_t phys_end)
>  
>  #ifdef __aarch64__
>  	init_alloc_vpage((void*)(4ul << 30));
> +
> +	assert_msg(system_supports_granule(PAGE_SIZE),
> +		   "Unsupported translation granule: %ld\n", PAGE_SIZE);
>  #endif
>  
>  	mmu_idmap = alloc_page();
> diff --git a/lib/arm64/asm/processor.h b/lib/arm64/asm/processor.h
> index 02665b84cc7e..dc493d1686bc 100644
> --- a/lib/arm64/asm/processor.h
> +++ b/lib/arm64/asm/processor.h
> @@ -117,5 +117,21 @@ static inline u64 get_ctr(void)
>  
>  extern u32 dcache_line_size;
>  
> +static inline unsigned long get_id_aa64mmfr0_el1(void)
> +{
> +	unsigned long mmfr0;
> +	asm volatile("mrs %0, id_aa64mmfr0_el1" : "=r" (mmfr0));
> +	return mmfr0;

I think we can safely use read_sysreg here, the other functions in this file do.

> +}
> +
> +static inline bool system_supports_granule(size_t granule)
> +{
> +	u64 mmfr0 = get_id_aa64mmfr0_el1();
> +
> +	return ((granule == SZ_4K && ((mmfr0 >> 28) & 0xf) == 0) ||
> +		(granule == SZ_64K && ((mmfr0 >> 24) & 0xf) == 0) ||
> +		(granule == SZ_16K && ((mmfr0 >> 20) & 0xf) == 1));
> +}

Or we can turn it into a switch statement and keep all the field defines. Either
way looks good to me (funny how tgran16 stands out).

Thanks,
Alex