Subject: Re: [PATCH V4 3/7] arm64/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

From: Catalin Marinas <[email-masked]>
Date: Fri, 8 Apr 2022 11:28:11 +0100

On Thu, Apr 07, 2022 at 04:02:47PM +0530, Anshuman Khandual wrote:
> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index 77ada00280d9..307534fcec00 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -55,3 +55,36 @@ static int __init adjust_protection_map(void)
>  	return 0;
>  }
>  arch_initcall(adjust_protection_map);
> +
> +static pgprot_t arm64_arch_vm_get_page_prot(unsigned long vm_flags)
> +{
> +	pteval_t prot = 0;
> +
> +	if (vm_flags & VM_ARM64_BTI)
> +		prot |= PTE_GP;
> +
> +	/*
> +	 * There are two conditions required for returning a Normal Tagged
> +	 * memory type: (1) the user requested it via PROT_MTE passed to
> +	 * mmap() or mprotect() and (2) the corresponding vma supports MTE. We
> +	 * register (1) as VM_MTE in the vma->vm_flags and (2) as
> +	 * VM_MTE_ALLOWED. Note that the latter can only be set during the
> +	 * mmap() call since mprotect() does not accept MAP_* flags.
> +	 * Checking for VM_MTE only is sufficient since arch_validate_flags()
> +	 * does not permit (VM_MTE & !VM_MTE_ALLOWED).
> +	 */
> +	if (vm_flags & VM_MTE)
> +		prot |= PTE_ATTRINDX(MT_NORMAL_TAGGED);
> +
> +	return __pgprot(prot);
> +}
> +
> +pgprot_t vm_get_page_prot(unsigned long vm_flags)
> +{
> +	pgprot_t ret = __pgprot(pgprot_val(protection_map[vm_flags &
> +				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
> +				pgprot_val(arm64_arch_vm_get_page_prot(vm_flags)));
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(vm_get_page_prot);

Could you write all this in a single function? I think I mentioned it in
a previous series (untested):

pgprot_t vm_get_page_prot(unsigned long vm_flags)
{
	pteval_t prot = pgprot_val(protection_map[vm_flags &
				   (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);

	if (vm_flags & VM_ARM64_BTI)
		prot |= PTE_GP;

	/*
	 * There are two conditions required for returning a Normal Tagged
	 * memory type: (1) the user requested it via PROT_MTE passed to
	 * mmap() or mprotect() and (2) the corresponding vma supports MTE. We
	 * register (1) as VM_MTE in the vma->vm_flags and (2) as
	 * VM_MTE_ALLOWED. Note that the latter can only be set during the
	 * mmap() call since mprotect() does not accept MAP_* flags.
	 * Checking for VM_MTE only is sufficient since arch_validate_flags()
	 * does not permit (VM_MTE & !VM_MTE_ALLOWED).
	 */
	if (vm_flags & VM_MTE)
		prot |= PTE_ATTRINDX(MT_NORMAL_TAGGED);

	return __pgprot(prot);
}
EXPORT_SYMBOL(vm_get_page_prot);

With that:

Reviewed-by: Catalin Marinas <[email-masked]>