Re: [PATCH v3 2/7] mm/vmalloc: Track which page-table levels were modified

Andrew Morton
2020-05-15T20:01:44Z

On Fri, 15 May 2020 16:00:18 +0200 Joerg Roedel <joro@8bytes.org> wrote:

> Track at which levels in the page-table entries were modified by
> vmap/vunmap. After the page-table has been modified, use that
> information do decide whether the new arch_sync_kernel_mappings()
> needs to be called.

Lots of collisions here with Christoph's "decruft the vmalloc API" series
(http://lkml.kernel.org/r/20200414131348.444715-1-hch@lst.de).

I attempted to fix things up.

unmap_kernel_range_noflush() needed to be redone.

map_kernel_range_noflush() might need the arch_sync_kernel_mappings() call?

From: Joerg Roedel <jroedel@suse.de>
Subject: mm/vmalloc: Track which page-table levels were modified

Track at which levels in the page-table entries were modified by
vmap/vunmap. After the page-table has been modified, use that information
do decide whether the new arch_sync_kernel_mappings() needs to be called.

Link: http://lkml.kernel.org/r/20200515140023.25469-3-joro@8bytes.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/vmalloc.h | 16 ++++++
mm/vmalloc.c | 91 +++++++++++++++++++++++++++-----------
2 files changed, 81 insertions(+), 26 deletions(-)

--- a/include/linux/vmalloc.h~mm-vmalloc-track-which-page-table-levels-were-modified
+++ a/include/linux/vmalloc.h
@@ -134,6 +134,22 @@ void vmalloc_sync_mappings(void);
void vmalloc_sync_unmappings(void);

/*
+ * Architectures can set this mask to a combination of PGTBL_P?D_MODIFIED values
+ * and let generic vmalloc and ioremap code know when arch_sync_kernel_mappings()
+ * needs to be called.
+ */
+#ifndef ARCH_PAGE_TABLE_SYNC_MASK
+#define ARCH_PAGE_TABLE_SYNC_MASK 0
+#endif
+
+/*
+ * There is no default implementation for arch_sync_kernel_mappings(). It is
+ * relied upon the compiler to optimize calls out if ARCH_PAGE_TABLE_SYNC_MASK
+ * is 0.
+ */
+void arch_sync_kernel_mappings(unsigned long start, unsigned long end);
+
+/*
* Lowlevel-APIs (not for driver use!)
*/

--- a/mm/vmalloc.c~mm-vmalloc-track-which-page-table-levels-were-modified
+++ a/mm/vmalloc.c
@@ -69,7 +69,8 @@ static void free_work(struct work_struct

/*** Page table manipulation functions ***/

-static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end)
+static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
+ pgtbl_mod_mask *mask)
{
pte_t *pte;

@@ -78,59 +79,81 @@ static void vunmap_pte_range(pmd_t *pmd,
pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte);
WARN_ON(!pte_none(ptent) && !pte_present(ptent));
} while (pte++, addr += PAGE_SIZE, addr != end);
+ *mask |= PGTBL_PTE_MODIFIED;
}

-static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end)
+static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
+ pgtbl_mod_mask *mask)
{
pmd_t *pmd;
unsigned long next;
+ int cleared;

pmd = pmd_offset(pud, addr);
do {
next = pmd_addr_end(addr, end);
- if (pmd_clear_huge(pmd))
+
+ cleared = pmd_clear_huge(pmd);
+ if (cleared || pmd_bad(*pmd))
+ *mask |= PGTBL_PMD_MODIFIED;
+
+ if (cleared)
continue;
if (pmd_none_or_clear_bad(pmd))
continue;
- vunmap_pte_range(pmd, addr, next);
+ vunmap_pte_range(pmd, addr, next, mask);
} while (pmd++, addr = next, addr != end);
}

-static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end)
+static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
+ pgtbl_mod_mask *mask)
{
pud_t *pud;
unsigned long next;
+ int cleared;

pud = pud_offset(p4d, addr);
do {
next = pud_addr_end(addr, end);
- if (pud_clear_huge(pud))
+
+ cleared = pud_clear_huge(pud);
+ if (cleared || pud_bad(*pud))
+ *mask |= PGTBL_PUD_MODIFIED;
+
+ if (cleared)
continue;
if (pud_none_or_clear_bad(pud))
continue;
- vunmap_pmd_range(pud, addr, next);
+ vunmap_pmd_range(pud, addr, next, mask);
} while (pud++, addr = next, addr != end);
}

-static void vunmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end)
+static void vunmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
+ pgtbl_mod_mask *mask)
{
p4d_t *p4d;
unsigned long next;
+ int cleared;

p4d = p4d_offset(pgd, addr);
do {
next = p4d_addr_end(addr, end);
- if (p4d_clear_huge(p4d))
+
+ cleared = p4d_clear_huge(p4d);
+ if (cleared || p4d_bad(*p4d))
+ *mask |= PGTBL_P4D_MODIFIED;
+
+ if (cleared)
continue;
if (p4d_none_or_clear_bad(p4d))
continue;
- vunmap_pud_range(p4d, addr, next);
+ vunmap_pud_range(p4d, addr, next, mask);
} while (p4d++, addr = next, addr != end);
}

/**
* unmap_kernel_range_noflush - unmap kernel VM area
- * @addr: start of the VM area to unmap
+ * @start: start of the VM area to unmap
* @size: size of the VM area to unmap
*
* Unmap PFN_UP(@size) pages at @addr. The VM area @addr and @size specify
@@ -141,24 +164,33 @@ static void vunmap_p4d_range(pgd_t *pgd,
* for calling flush_cache_vunmap() on to-be-mapped areas before calling this
* function and flush_tlb_kernel_range() after.
*/
-void unmap_kernel_range_noflush(unsigned long addr, unsigned long size)
+void unmap_kernel_range_noflush(unsigned long start, unsigned long size)
{
- unsigned long end = addr + size;
+ unsigned long end = start + size;
unsigned long next;
pgd_t *pgd;
+ unsigned long addr = start;
+ pgtbl_mod_mask mask = 0;

BUG_ON(addr >= end);
+ start = addr;
pgd = pgd_offset_k(addr);
do {
next = pgd_addr_end(addr, end);
+ if (pgd_bad(*pgd))
+ mask |= PGTBL_PGD_MODIFIED;
if (pgd_none_or_clear_bad(pgd))
continue;
- vunmap_p4d_range(pgd, addr, next);
+ vunmap_p4d_range(pgd, addr, next, &mask);
} while (pgd++, addr = next, addr != end);
+
+ if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
+ arch_sync_kernel_mappings(start, end);
}

static int vmap_pte_range(pmd_t *pmd, unsigned long addr,
- unsigned long end, pgprot_t prot, struct page **pages, int *nr)
+ unsigned long end, pgprot_t prot, struct page **pages, int *nr,
+ pgtbl_mod_mask *mask)
{
pte_t *pte;

@@ -167,7 +199,7 @@ static int vmap_pte_range(pmd_t *pmd, un
* callers keep track of where we're up to.
*/

- pte = pte_alloc_kernel(pmd, addr);
+ pte = pte_alloc_kernel_track(pmd, addr, mask);
if (!pte)
return -ENOMEM;
do {
@@ -180,55 +212,59 @@ static int vmap_pte_range(pmd_t *pmd, un
set_pte_at(&init_mm, addr, pte, mk_pte(page, prot));
(*nr)++;
} while (pte++, addr += PAGE_SIZE, addr != end);
+ *mask |= PGTBL_PTE_MODIFIED;
return 0;
}

static int vmap_pmd_range(pud_t *pud, unsigned long addr,
- unsigned long end, pgprot_t prot, struct page **pages, int *nr)
+ unsigned long end, pgprot_t prot, struct page **pages, int *nr,
+ pgtbl_mod_mask *mask)
{
pmd_t *pmd;
unsigned long next;

- pmd = pmd_alloc(&init_mm, pud, addr);
+ pmd = pmd_alloc_track(&init_mm, pud, addr, mask);
if (!pmd)
return -ENOMEM;
do {
next = pmd_addr_end(addr, end);
- if (vmap_pte_range(pmd, addr, next, prot, pages, nr))
+ if (vmap_pte_range(pmd, addr, next, prot, pages, nr, mask))
return -ENOMEM;
} while (pmd++, addr = next, addr != end);
return 0;
}

static int vmap_pud_range(p4d_t *p4d, unsigned long addr,
- unsigned long end, pgprot_t prot, struct page **pages, int *nr)
+ unsigned long end, pgprot_t prot, struct page **pages, int *nr,
+ pgtbl_mod_mask *mask)
{
pud_t *pud;
unsigned long next;

- pud = pud_alloc(&init_mm, p4d, addr);
+ pud = pud_alloc_track(&init_mm, p4d, addr, mask);
if (!pud)
return -ENOMEM;
do {
next = pud_addr_end(addr, end);
- if (vmap_pmd_range(pud, addr, next, prot, pages, nr))
+ if (vmap_pmd_range(pud, addr, next, prot, pages, nr, mask))
return -ENOMEM;
} while (pud++, addr = next, addr != end);
return 0;
}

static int vmap_p4d_range(pgd_t *pgd, unsigned long addr,
- unsigned long end, pgprot_t prot, struct page **pages, int *nr)
+ unsigned long end, pgprot_t prot, struct page **pages, int *nr,
+ pgtbl_mod_mask *mask)
{
p4d_t *p4d;
unsigned long next;

- p4d = p4d_alloc(&init_mm, pgd, addr);
+ p4d = p4d_alloc_track(&init_mm, pgd, addr, mask);
if (!p4d)
return -ENOMEM;
do {
next = p4d_addr_end(addr, end);
- if (vmap_pud_range(p4d, addr, next, prot, pages, nr))
+ if (vmap_pud_range(p4d, addr, next, prot, pages, nr, mask))
return -ENOMEM;
} while (p4d++, addr = next, addr != end);
return 0;
@@ -260,12 +296,15 @@ int map_kernel_range_noflush(unsigned lo
pgd_t *pgd;
int err = 0;
int nr = 0;
+ pgtbl_mod_mask mask = 0;

BUG_ON(addr >= end);
pgd = pgd_offset_k(addr);
do {
next = pgd_addr_end(addr, end);
- err = vmap_p4d_range(pgd, addr, next, prot, pages, &nr);
+ if (pgd_bad(*pgd))
+ mask |= PGTBL_PGD_MODIFIED;
+ err = vmap_p4d_range(pgd, addr, next, prot, pages, &nr, &mask);
if (err)
return err;
} while (pgd++, addr = next, addr != end);
_