Re: [PATCH] arm64: Add support for PTE contiguous bit.

From: David Woods
Date: Mon Sep 21 2015 - 13:03:57 EST


Steve,

Thanks for your review and comments. I take your points about the 16k granule - it's helpful to know that support is in the works. However, I'm not sure I agree with your reading of section 4.4.2. It's clear that for 16k granules, the number of contiguous pages is different for the PTE and PMD levels. But I don't see anywhere it says that for 4K and 64K that the contig bit is not supported at the PMD level - just that the number of contiguous pages is the same at each level.

I tried using the tarmac trace module of the ARM simulator to support this idea by turning on MMU tracing. Using 4k granule, I created 64k and 32m pages and touched each location in the page. In both cases, the trace recorded just one TLB fill (rather than the 16 you'd expect if the contiguous bit were being ignored) and it indicated the expected page size.

1817498494 clk cpu2 TLB FILL cpu2.S1TLB 64K 0x2000000000_NS vmid=0, nG asid=303:0x08fa360000_NS Normal InnerShareable Inner=WriteBackWriteAllocate Outer=WriteBackWriteAllocate xn=0 pxn=1 ContiguousHint=1

1263366314 clk cpu2 TLB FILL cpu2.UTLB 32M 0x2000000000_NS vmid=0, nG asid=300:0x08f6000000_NS Normal InnerShareable Inner=WriteBackWriteAllocate Outer=WriteBackWriteAllocate xn=0 pxn=1 ContiguousHint=1

I'll try this with a 64k granule next. I'm not sure what will happen with 16G pages since we are using an A53 model which I don't think supports such large pages.

-Dave

On 09/16/2015 04:46 AM, Steve Capper wrote:
On 15 September 2015 at 19:01, David Woods <dwoods@xxxxxxxxxx> wrote:
The arm64 MMU supports a Contiguous bit which is a hint that the TTE
is one of a set of contiguous entries which can be cached in a single
TLB entry. Supporting this bit adds new intermediate huge page sizes.

The set of huge page sizes available depends on the base page size.
Without using contiguous pages the huge page sizes are as follows.

4KB: 2MB 1GB
64KB: 512MB 4TB
We just have 512MB for a 64KB granule.
As per [1] D4.2.6 - "The VMSAv8-64 translation table format" page D4-1668.

With 4KB pages, the contiguous bit groups together sets of 16 pages
and with 64KB pages it groups sets of 32 pages. This enables two new
huge page sizes in each case, so that the full set of available sizes
is as follows.

4KB: 64KB 2MB 32MB 1GB
64KB: 2MB 512MB 16GB 4TB

If the base page size is set to 64KB then 2MB pages are enabled by
default. It is possible in the future to make 2MB the default huge
page size for both 4KB and 64KB pages.

Hi David,
Thanks for posting this, and apologies in advance for talking about
the ARM ARM[1]...

D4.4.2 "Other fields in the VMSAv8-64 translation table format
descriptors" (page D4-1715)
Only gives examples of the contiguous bit being used for level 3
descriptors (i.e. PTEs) when running with a 4KB and 64KB granule.

With a 16KB granule we *can* have a contiguous bit being used by level
2 descriptors (i.e. PMDs), so the pmd_contig logic could perhaps be
used in combination with Suzuki's 16KB PAGE_SIZE series at:
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-September/370117.html

I will read through the rest of the patch and post more feedback

Cheers,
--
Steve

[1] - http://infocenter.arm.com/help/topic/com.arm.doc.ddi0487a.g/index.html




Signed-off-by: David Woods <dwoods@xxxxxxxxxx>
Reviewed-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
---
arch/arm64/Kconfig | 3 -
arch/arm64/include/asm/hugetlb.h | 4 +
arch/arm64/include/asm/pgtable-hwdef.h | 15 +++
arch/arm64/include/asm/pgtable.h | 30 +++++-
arch/arm64/mm/hugetlbpage.c | 165 ++++++++++++++++++++++++++++++++-
5 files changed, 210 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7d95663..8310e38 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -447,9 +447,6 @@ config HW_PERF_EVENTS
config SYS_SUPPORTS_HUGETLBFS
def_bool y

-config ARCH_WANT_GENERAL_HUGETLB
- def_bool y
-
config ARCH_WANT_HUGE_PMD_SHARE
def_bool y if !ARM64_64K_PAGES

diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index bb4052e..e5af553 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -97,4 +97,8 @@ static inline void arch_clear_hugepage_flags(struct page *page)
clear_bit(PG_dcache_clean, &page->flags);
}

+extern pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
+ struct page *page, int writable);
+#define arch_make_huge_pte arch_make_huge_pte
+
#endif /* __ASM_HUGETLB_H */
diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index 24154b0..da73243 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -55,6 +55,19 @@
#define SECTION_MASK (~(SECTION_SIZE-1))

/*
+ * Contiguous large page definitions.
+ */
+#ifdef CONFIG_ARM64_64K_PAGES
+#define CONTIG_SHIFT 5
+#define CONTIG_PAGES 32
+#else
+#define CONTIG_SHIFT 4
+#define CONTIG_PAGES 16
+#endif
+#define CONTIG_PTE_SIZE (CONTIG_PAGES * PAGE_SIZE)
+#define CONTIG_PTE_MASK (~(CONTIG_PTE_SIZE - 1))
+
+/*
* Hardware page table definitions.
*
* Level 1 descriptor (PUD).
@@ -83,6 +96,7 @@
#define PMD_SECT_S (_AT(pmdval_t, 3) << 8)
#define PMD_SECT_AF (_AT(pmdval_t, 1) << 10)
#define PMD_SECT_NG (_AT(pmdval_t, 1) << 11)
+#define PMD_SECT_CONTIG (_AT(pmdval_t, 1) << 52)
#define PMD_SECT_PXN (_AT(pmdval_t, 1) << 53)
#define PMD_SECT_UXN (_AT(pmdval_t, 1) << 54)

@@ -105,6 +119,7 @@
#define PTE_AF (_AT(pteval_t, 1) << 10) /* Access Flag */
#define PTE_NG (_AT(pteval_t, 1) << 11) /* nG */
#define PTE_DBM (_AT(pteval_t, 1) << 51) /* Dirty Bit Management */
+#define PTE_CONTIG (_AT(pteval_t, 1) << 52) /* Contiguous */
#define PTE_PXN (_AT(pteval_t, 1) << 53) /* Privileged XN */
#define PTE_UXN (_AT(pteval_t, 1) << 54) /* User XN */

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 6900b2d9..df5ec64 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -144,6 +144,7 @@ extern struct page *empty_zero_page;
#define pte_special(pte) (!!(pte_val(pte) & PTE_SPECIAL))
#define pte_write(pte) (!!(pte_val(pte) & PTE_WRITE))
#define pte_exec(pte) (!(pte_val(pte) & PTE_UXN))
+#define pte_contig(pte) (!!(pte_val(pte) & PTE_CONTIG))

#ifdef CONFIG_ARM64_HW_AFDBM
#define pte_hw_dirty(pte) (!(pte_val(pte) & PTE_RDONLY))
@@ -206,6 +207,9 @@ static inline pte_t pte_mkspecial(pte_t pte)
return set_pte_bit(pte, __pgprot(PTE_SPECIAL));
}

+extern pte_t pte_mkcontig(pte_t pte);
+extern pmd_t pmd_mkcontig(pmd_t pmd);
+
static inline void set_pte(pte_t *ptep, pte_t pte)
{
*ptep = pte;
@@ -275,7 +279,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
/*
* Hugetlb definitions.
*/
-#define HUGE_MAX_HSTATE 2
+#define HUGE_MAX_HSTATE ((2 * CONFIG_PGTABLE_LEVELS) - 1)
#define HPAGE_SHIFT PMD_SHIFT
#define HPAGE_SIZE (_AC(1, UL) << HPAGE_SHIFT)
#define HPAGE_MASK (~(HPAGE_SIZE - 1))
@@ -372,7 +376,8 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
#define pmd_none(pmd) (!pmd_val(pmd))
#define pmd_present(pmd) (pmd_val(pmd))

-#define pmd_bad(pmd) (!(pmd_val(pmd) & 2))
+#define pmd_bad(pmd) (!(pmd_val(pmd) & \
+ (PMD_TABLE_BIT | PMD_SECT_CONTIG)))

#define pmd_table(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \
PMD_TYPE_TABLE)
@@ -500,7 +505,8 @@ static inline pud_t *pud_offset(pgd_t *pgd, unsigned long addr)
static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
{
const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
- PTE_PROT_NONE | PTE_WRITE | PTE_TYPE_MASK;
+ PTE_PROT_NONE | PTE_WRITE | PTE_TYPE_MASK |
+ PTE_CONTIG;
/* preserve the hardware dirty information */
if (pte_hw_dirty(pte))
newprot |= PTE_DIRTY;
@@ -513,6 +519,24 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
return pte_pmd(pte_modify(pmd_pte(pmd), newprot));
}

+static inline pte_t pte_modify_pfn(pte_t pte, unsigned long newpfn)
+{
+ const pteval_t mask = PHYS_MASK & PAGE_MASK;
+
+ pte_val(pte) = pfn_pte(newpfn, (pte_val(pte) & ~mask));
+ return pte;
+}
+
+#if CONFIG_PGTABLE_LEVELS > 2
+static inline pmd_t pmd_modify_pfn(pmd_t pmd, unsigned long newpfn)
+{
+ const pmdval_t mask = PHYS_MASK & PAGE_MASK;
+
+ pmd = pfn_pmd(newpfn, (pmd_val(pmd) & ~mask));
+ return pmd;
+}
+#endif
+
#ifdef CONFIG_ARM64_HW_AFDBM
/*
* Atomic pte/pmd modifications.
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 383b03f..f5bbbbc 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -41,6 +41,155 @@ int pud_huge(pud_t pud)
#endif
}

+pte_t *huge_pte_alloc(struct mm_struct *mm,
+ unsigned long addr, unsigned long sz)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pte_t *pte = NULL;
+ int i;
+
+ pgd = pgd_offset(mm, addr);
+ pud = pud_alloc(mm, pgd, addr);
+ if (pud) {
+ if (sz == PUD_SIZE) {
+ pte = (pte_t *)pud;
+ } else if (sz == PMD_SIZE) {
+#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
+ if (pud_none(*pud))
+ pte = huge_pmd_share(mm, addr, pud);
+ else
+#endif
+ pte = (pte_t *)pmd_alloc(mm, pud, addr);
+ } else if (sz == (PAGE_SIZE * CONTIG_PAGES)) {
+ pmd_t *pmd = pmd_alloc(mm, pud, addr);
+
+ WARN_ON(addr & (sz - 1));
+ pte = pte_alloc_map(mm, NULL, pmd, addr);
+ if (pte_present(*pte)) {
+ unsigned long pfn;
+ *pte = pte_mkcontig(*pte);
+ pfn = pte_pfn(*pte);
+ for (i = 0; i < CONTIG_PAGES; i++) {
+ set_pte(&pte[i],
+ pte_modify_pfn(*pte, pfn + i));
+ }
+ }
+#if CONFIG_PGTABLE_LEVELS > 2
+ } else if (sz == (PMD_SIZE * CONTIG_PAGES)) {
+ pmd_t *pmd;
+
+ pmd = pmd_alloc(mm, pud, addr);
+ WARN_ON(addr & (sz - 1));
+ if (pmd && pmd_present(*pmd)) {
+ unsigned long pfn;
+ pmd_t pmdval;
+
+ pmdval = *pmd = pmd_mkcontig(*pmd);
+ pfn = pmd_pfn(*pmd);
+ for (i = 0; i < CONTIG_PAGES; i++) {
+ unsigned long newpfn = pfn +
+ (i << (PMD_SHIFT - PAGE_SHIFT));
+ if (!pmd_present(pmd[i]))
+ atomic_long_inc(&mm->nr_ptes);
+ set_pmd(&pmd[i],
+ pmd_modify_pfn(pmdval, newpfn));
+ }
+ }
+ return pmd;
+#endif
+ }
+ }
+
+ return pte;
+}
+
+pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd = NULL;
+ pte_t *pte = NULL;
+
+ pgd = pgd_offset(mm, addr);
+ if (pgd_present(*pgd)) {
+ pud = pud_offset(pgd, addr);
+ if (pud_present(*pud)) {
+ if (pud_huge(*pud))
+ return (pte_t *)pud;
+ pmd = pmd_offset(pud, addr);
+ if (pmd_present(*pmd)) {
+ if (pmd_huge(*pmd))
+ return (pte_t *)pmd;
+ pte = pte_offset_kernel(pmd, addr);
+ if (pte_present(*pte) && pte_contig(*pte)) {
+ pte = pte_offset_kernel(
+ pmd, (addr & CONTIG_PTE_MASK));
+ return pte;
+ }
+ }
+ }
+ }
+ return (pte_t *) NULL;
+}
+
+pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
+ struct page *page, int writable)
+{
+ size_t pagesize = huge_page_size(hstate_vma(vma));
+ pte_t nent = {0};
+
+ if (pagesize == PUD_SIZE || pagesize == PMD_SIZE)
+ nent = entry;
+ else if (pagesize == (PAGE_SIZE * CONTIG_PAGES))
+ nent = pte_mkcontig(entry);
+#if CONFIG_PGTABLE_LEVELS > 2
+ else if (pagesize == (PMD_SIZE * CONTIG_PAGES) ||
+ pagesize == (PUD_SIZE * CONTIG_PAGES))
+ nent = pmd_mkcontig(entry);
+#endif
+ else {
+ pr_warn("%s: unrecognized huge page size 0x%lx\n",
+ __func__, pagesize);
+ }
+ return nent;
+}
+
+pte_t pte_mkcontig(pte_t pte)
+{
+ pte = set_pte_bit(pte, __pgprot(PTE_CONTIG));
+ pte = set_pte_bit(pte, __pgprot(PTE_TYPE_PAGE));
+ return pte;
+}
+
+pmd_t pmd_mkcontig(pmd_t pmd)
+{
+ pmd = __pmd(pmd_val(pmd) | PMD_SECT_CONTIG);
+ return pmd;
+}
+
+struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
+ pmd_t *pmd, int write)
+{
+ struct page *page;
+
+ page = pte_page(*(pte_t *)pmd);
+ if (page)
+ page += ((address & ~PMD_MASK) >> PAGE_SHIFT);
+ return page;
+}
+
+struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,
+ pud_t *pud, int write)
+{
+ struct page *page;
+
+ page = pte_page(*(pte_t *)pud);
+ if (page)
+ page += ((address & ~PUD_MASK) >> PAGE_SHIFT);
+ return page;
+}
+
static __init int setup_hugepagesz(char *opt)
{
unsigned long ps = memparse(opt, &opt);
@@ -48,10 +197,24 @@ static __init int setup_hugepagesz(char *opt)
hugetlb_add_hstate(PMD_SHIFT - PAGE_SHIFT);
} else if (ps == PUD_SIZE) {
hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
+ } else if (ps == (PAGE_SIZE * CONTIG_PAGES)) {
+ hugetlb_add_hstate(CONTIG_SHIFT);
+ } else if (ps == (PMD_SIZE * CONTIG_PAGES)) {
+ hugetlb_add_hstate((PMD_SHIFT + CONTIG_SHIFT) - PAGE_SHIFT);
} else {
- pr_err("hugepagesz: Unsupported page size %lu M\n", ps >> 20);
+ pr_err("hugepagesz: Unsupported page size %lu K\n", ps >> 10);
return 0;
}
return 1;
}
__setup("hugepagesz=", setup_hugepagesz);
+
+#ifdef CONFIG_ARM64_64K_PAGES
+static __init int add_default_hugepagesz(void)
+{
+ if (size_to_hstate(CONTIG_PAGES * PAGE_SIZE) == NULL)
+ hugetlb_add_hstate(CONTIG_SHIFT);
+ return 0;
+}
+arch_initcall(add_default_hugepagesz);
+#endif
--
2.1.2


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