Re: [PATCH] arm64: mte: Use PAGE_KERNEL_TAGGED in arch_add_memory

[David Hildenbrand <david@redhat.com>]

On 05.03.21 18:44, Catalin Marinas wrote:
> On Fri, Mar 05, 2021 at 04:55:28PM +0100, David Hildenbrand wrote:
>> On 05.03.21 16:43, Catalin Marinas wrote:
>>> On Fri, Mar 05, 2021 at 11:19:08AM +0000, Catalin Marinas wrote:
>>>> On Tue, Mar 02, 2021 at 08:21:03PM -0800, Patrick Daly wrote:
>>>>> In a system which supports MTE, the linear kernel region must allow
>>>>> reading/writing allocation tags. For memory present at boot this
>>>>> is already being done in map_mem(). Add the same in arch_add_memory().
>>>>>
>>>>> Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
>>>>> ---
>>>>>    arch/arm64/mm/mmu.c | 12 +++++++++++-
>>>>>    1 file changed, 11 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>>>>> index 9b25d60b..0fcfe90 100644
>>>>> --- a/arch/arm64/mm/mmu.c
>>>>> +++ b/arch/arm64/mm/mmu.c
>>>>> @@ -1463,6 +1463,7 @@ int arch_add_memory(int nid, u64 start, u64 size,
>>>>>    		    struct mhp_params *params)
>>>>>    {
>>>>>    	int ret, flags = 0;
>>>>> +	pgprot_t pgprot;
>>>>>    	if (!inside_linear_region(start, size)) {
>>>>>    		pr_err("[%llx %llx] is outside linear mapping region\n", start, start + size);
>>>>> @@ -1477,8 +1478,17 @@ int arch_add_memory(int nid, u64 start, u64 size,
>>>>>    	    IS_ENABLED(CONFIG_KFENCE))
>>>>>    		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>>>>> +	/*
>>>>> +	 * The linear map must allow allocation tags reading/writing
>>>>> +	 * if MTE is present. Otherwise, it has the same attributes as
>>>>> +	 * PAGE_KERNEL.
>>>>> +	 */
>>>>> +	pgprot = params->pgprot;
>>>>> +	if (pgprot_val(pgprot) == pgprot_val(PAGE_KERNEL))
>>>>> +		pgprot = PAGE_KERNEL_TAGGED;
>>>>> +
>>>>>    	__create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
>>>>> -			     size, params->pgprot, __pgd_pgtable_alloc,
>>>>> +			     size, pgprot, __pgd_pgtable_alloc,
>>>>>    			     flags);
> [...]
>>> ---------------8<-------------------------------
>>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
>>> index e17b96d0e4b5..5c78b92d9ec5 100644
>>> --- a/arch/arm64/include/asm/pgtable.h
>>> +++ b/arch/arm64/include/asm/pgtable.h
>>> @@ -486,6 +486,8 @@ static inline pmd_t pmd_mkdevmap(pmd_t pmd)
>>>    	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_NORMAL_NC) | PTE_PXN | PTE_UXN)
>>>    #define pgprot_device(prot) \
>>>    	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_DEVICE_nGnRE) | PTE_PXN | PTE_UXN)
>>> +#define pgprot_tagged(prot) \
>>> +	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_NORMAL_TAGGED))
>>>    /*
>>>     * DMA allocations for non-coherent devices use what the Arm architecture calls
>>>     * "Normal non-cacheable" memory, which permits speculation, unaligned accesses
>>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>>> index cdfc4e9f253e..f5f5044db2ce 100644
>>> --- a/include/linux/pgtable.h
>>> +++ b/include/linux/pgtable.h
>>> @@ -904,6 +904,10 @@ static inline void ptep_modify_prot_commit(struct vm_area_struct *vma,
>>>    #define pgprot_device pgprot_noncached
>>>    #endif
>>>
>>> +#ifndef pgprot_tagged
>>> +#define pgprot_tagged(prot)	(prot)
>>> +#endif
>>> +
>>>    #ifdef CONFIG_MMU
>>>    #ifndef pgprot_modify
>>>    #define pgprot_modify pgprot_modify
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 5ba51a8bdaeb..4253d80a59ba 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -1072,7 +1072,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
>>>     */
>>>    int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
>>>    {
>>> -	struct mhp_params params = { .pgprot = PAGE_KERNEL };
>>> +	struct mhp_params params = { .pgprot = pgprot_tagged(PAGE_KERNEL) };
>>
>> This looks like we're pushing arch specific stuff ("tagged") in here. Can't
>> we generalize this to something like
>>
>> pgprot_mhp_default
>>
>> (or a better name)
>>
>> that defaults to PAGE_KERNEL on all architectures except arm64 which
>> overwrites this somehow?
> 
> It works for me but I prefer the prot modification style similar to
> pgprot_writecombine() etc. (i.e. takes a parameter like PAGE_KERNEL and
> just changes bits of it).

Sure, I'm wondering if we can abstract the "tagged" part here.

pgprot_mhp(PAGE_KERNEL) whatsoever.

But maybe we do consider the "tagged" part okay in common code already 
(it felt quite arm64 specific to me at first). I can spot 
untagged_addr() all over the place. So maybe pgprot_tagged() is just fine.

-- 
Thanks,

David / dhildenb