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

[Ritesh Harjani (IBM)]

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 at gmail.com>
---

@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