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xen: lock pte pages while pinning/unpinning

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When a pagetable is created, it is made globally visible in the rmap
prio tree before it is pinned via arch_dup_mmap(), and remains in the
rmap tree while it is unpinned with arch_exit_mmap().

This means that other CPUs may race with the pinning/unpinning
process, and see a pte between when it gets marked RO and actually
pinned, causing any pte updates to fail with write-protect faults.

As a result, all pte pages must be properly locked, and only unlocked
once the pinning/unpinning process has finished.

In order to avoid taking spinlocks for the whole pagetable - which may
overflow the PREEMPT_BITS portion of preempt counter - it locks and pins
each pte page individually, and then finally pins the whole pagetable.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickens <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <ak@suse.de>
Cc: Keir Fraser <keir@xensource.com>
Cc: Jan Beulich <jbeulich@novell.com>
This commit is contained in:
Jeremy Fitzhardinge
2007-10-16 11:51:30 -07:00
committed by Jeremy Fitzhardinge
parent 9f79991d41
commit 74260714c5
3 changed files with 103 additions and 41 deletions
Download Patch File Download Diff File Expand all files Collapse all files

30
arch/x86/xen/enlighten.c
View File

@@ -666,6 +666,15 @@ static __init void xen_alloc_pt_init(struct mm_struct *mm, u32 pfn)
make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
}
static void pin_pagetable_pfn(unsigned level, unsigned long pfn)
{
struct mmuext_op op;
op.cmd = level;
op.arg1.mfn = pfn_to_mfn(pfn);
if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
BUG();
}
/* This needs to make sure the new pte page is pinned iff its being
attached to a pinned pagetable. */
static void xen_alloc_pt(struct mm_struct *mm, u32 pfn)
@@ -675,9 +684,10 @@ static void xen_alloc_pt(struct mm_struct *mm, u32 pfn)
if (PagePinned(virt_to_page(mm->pgd))) {
SetPagePinned(page);
if (!PageHighMem(page))
if (!PageHighMem(page)) {
make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
else
pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);
} else
/* make sure there are no stray mappings of
this page */
kmap_flush_unused();
@@ -690,8 +700,10 @@ static void xen_release_pt(u32 pfn)
struct page *page = pfn_to_page(pfn);
if (PagePinned(page)) {
if (!PageHighMem(page))
if (!PageHighMem(page)) {
pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
}
}
}
@@ -806,15 +818,15 @@ static __init void xen_pagetable_setup_done(pgd_t *base)
/* Actually pin the pagetable down, but we can't set PG_pinned
yet because the page structures don't exist yet. */
{
struct mmuext_op op;
unsigned level;
#ifdef CONFIG_X86_PAE
op.cmd = MMUEXT_PIN_L3_TABLE;
level = MMUEXT_PIN_L3_TABLE;
#else
op.cmd = MMUEXT_PIN_L3_TABLE;
level = MMUEXT_PIN_L2_TABLE;
#endif
op.arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(base)));
if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
BUG();
pin_pagetable_pfn(level, PFN_DOWN(__pa(base)));
}
}