> Differentiate between hardware not supporting hugepages and user disabling THP
> via 'echo never > /sys/kernel/mm/transparent_hugepage/enabled'
>
> For the devdax namespace, the kernel handles the above via the
> supported_alignment attribute and failing to initialize the namespace
> if the namespace align value is not supported on the platform.
>
> For the fsdax namespace, the kernel will continue to initialize
> the namespace. This can result in the kernel creating a huge pte
> entry even though the hardware don't support the same.
>
> We do want hugepage support with pmem even if the end-user disabled THP
> via sysfs file (/sys/kernel/mm/transparent_hugepage/enabled). Hence
> differentiate between hardware/firmware lacking support vs user-controlled
> disable of THP and prevent a huge fault if the hardware lacks hugepage
> support.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> ---
> include/linux/huge_mm.h | 15 +++++++++------
> mm/huge_memory.c | 6 +++++-
> 2 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 6a19f35f836b..ba973efcd369 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -78,6 +78,7 @@ static inline vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn,
> }
>
> enum transparent_hugepage_flag {
> + TRANSPARENT_HUGEPAGE_NEVER_DAX,
> TRANSPARENT_HUGEPAGE_FLAG,
> TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
> @@ -123,6 +124,13 @@ extern unsigned long transparent_hugepage_flags;
> */
> static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
> {
> +
> + /*
> + * If the hardware/firmware marked hugepage support disabled.
> + */
> + if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_NEVER_DAX))
> + return false;
> +
> if (vma->vm_flags & VM_NOHUGEPAGE)
> return false;
>
> @@ -134,12 +142,7 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>
> if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG))
> return true;
> - /*
> - * For dax vmas, try to always use hugepage mappings. If the kernel does
> - * not support hugepages, fsdax mappings will fallback to PAGE_SIZE
> - * mappings, and device-dax namespaces, that try to guarantee a given
> - * mapping size, will fail to enable
> - */
> +
> if (vma_is_dax(vma))
> return true;
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9237976abe72..d698b7e27447 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -386,7 +386,11 @@ static int __init hugepage_init(void)
> struct kobject *hugepage_kobj;
>
> if (!has_transparent_hugepage()) {
> - transparent_hugepage_flags = 0;
> + /*
> + * Hardware doesn't support hugepages, hence disable
> + * DAX PMD support.
> + */
> + transparent_hugepage_flags = 1 << TRANSPARENT_HUGEPAGE_NEVER_DAX;
> return -EINVAL;
> }
Reviewed-by: Pankaj Gupta <pankaj.gupta@xxxxxxxxxxxxxxx>
