Re: [RFC v1 2/2] powerpc/64s: Add support for huge pfnmaps

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 27/02/2026 à 07:16, Ritesh Harjani (IBM) a écrit :
> This uses _RPAGE_SW2 bit for the PMD and PUDs similar to PTEs.
> This also adds support for {pte,pmd,pud}_pgprot helpers needed for
> follow_pfnmap APIs.
> 
> This allows us to extend the PFN mappings, e.g. PCI MMIO bars where
> it can grow as large as 8GB or even bigger, to map at PMD / PUD level.
> VFIO PCI core driver already supports fault handling at PMD / PUD level
> for more efficient BAR mappings.
> 
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>


> ---
> 
> @linux-mm:
> Is there any official test which I could use to verify this functionality.
> 
> For now I used basic ivshmem setup + vfio using Qemu and validated using some
> basic test to see that we are seeing these prints.
> 
> [ 4351.435050] vfio_pci_mmap_huge_fault: 3 callbacks suppressed
> [ 4351.435234] vfio-pci 0001:00:00.0: vfio_pci_mmap_huge_fault(,order = 5) BAR 2 page offset 0x0: 0x100
> [ 4351.457005] vfio-pci 0001:00:00.0: vfio_pci_mmap_huge_fault(,order = 5) BAR 2 page offset 0x40: 0x100
> [ 4351.463684] vfio-pci 0001:00:00.0: vfio_pci_mmap_huge_fault(,order = 5) BAR 2 page offset 0x20: 0x100
> 
>   arch/powerpc/Kconfig                         |  1 +
>   arch/powerpc/include/asm/book3s/64/pgtable.h | 23 ++++++++++++++++++++
>   arch/powerpc/include/asm/pgtable.h           | 12 ++++++++++
>   3 files changed, 36 insertions(+)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index ad7a2fe63a2a..cf9283757e5d 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -172,6 +172,7 @@ config PPC
>   	select ARCH_STACKWALK
>   	select ARCH_SUPPORTS_ATOMIC_RMW
>   	select ARCH_SUPPORTS_DEBUG_PAGEALLOC	if PPC_BOOK3S || PPC_8xx
> +	select ARCH_SUPPORTS_HUGE_PFNMAP	if PPC_BOOK3S_64 && TRANSPARENT_HUGEPAGE
>   	select ARCH_SUPPORTS_PAGE_TABLE_CHECK	if !HUGETLB_PAGE
>   	select ARCH_SUPPORTS_SCHED_MC		if SMP
>   	select ARCH_SUPPORTS_SCHED_SMT		if PPC64 && SMP
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 1a91762b455d..639cbf34f752 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -1289,6 +1289,29 @@ static inline pud_t pud_mkhuge(pud_t pud)
>   	return pud;
>   }
> 
> +#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
> +static inline bool pmd_special(pmd_t pmd)
> +{
> +	return pte_special(pmd_pte(pmd));
> +}
> +
> +static inline pmd_t pmd_mkspecial(pmd_t pmd)
> +{
> +	return pte_pmd(pte_mkspecial(pmd_pte(pmd)));
> +}
> +#endif
> +
> +#ifdef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
> +static inline bool pud_special(pud_t pud)
> +{
> +	return pte_special(pud_pte(pud));
> +}
> +
> +static inline pud_t pud_mkspecial(pud_t pud)
> +{
> +	return pte_pud(pte_mkspecial(pud_pte(pud)));
> +}
> +#endif
> 
>   #define __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
>   extern int pmdp_set_access_flags(struct vm_area_struct *vma,
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index dcd3a88caaf6..2d27cb1c2334 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -63,6 +63,18 @@ static inline pgprot_t pte_pgprot(pte_t pte)
>   	return __pgprot(pte_flags);
>   }
> 
> +#define pmd_pgprot pmd_pgprot
> +static inline pgprot_t pmd_pgprot(pmd_t pmd)
> +{
> +	return pte_pgprot(pmd_pte(pmd));
> +}
> +
> +#define pud_pgprot pud_pgprot
> +static inline pgprot_t pud_pgprot(pud_t pud)
> +{
> +	return pte_pgprot(pud_pte(pud));
> +}
> +
>   static inline pgprot_t pgprot_nx(pgprot_t prot)
>   {
>   	return pte_pgprot(pte_exprotect(__pte(pgprot_val(prot))));
> --
> 2.53.0
> 
>