On Thu, Jun 11, 2009 at 09:27:09PM +0300, Pasi Kärkkäinen wrote:
> On Thu, Jun 11, 2009 at 10:18:34AM +0100, Ian Campbell wrote:
> > Pasi, to validate the theory that you are seeing races between unpinning
> > and kmap_atomic_pte can you give this biguglystick approach to solving
> > it a go.
> >
>
> Guess what..
>
> Now my dom0 didn't crash !! (with only this patch applied).
> It survived kernel compilation just fine.. first time so far with pv_ops dom0.
>
> I'll try again, just in case.
>
Yep, I tried again, and it still worked.
No crashes anymore with this patch :) Congratulations and thanks!
-- Pasi
>
> > diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> > index 1729178..beeb8e8 100644
> > --- a/arch/x86/xen/mmu.c
> > +++ b/arch/x86/xen/mmu.c
> > @@ -1145,9 +1145,12 @@ static int xen_unpin_page(struct mm_struct *mm,
> > struct page *page,
> > return 0; /* never need to flush on unpin */
> > }
> >
> > +static DEFINE_SPINLOCK(hack_lock); /* Hack to sync unpin against
> > kmap_atomic_pte */
> > +
> > /* Release a pagetables pages back as normal RW */
> > static void __xen_pgd_unpin(struct mm_struct *mm, pgd_t *pgd)
> > {
> > + spin_lock(&hack_lock);
> > xen_mc_batch();
> >
> > xen_do_pin(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));
> > @@ -1173,6 +1176,7 @@ static void __xen_pgd_unpin(struct mm_struct *mm,
> > pgd_t *pgd)
> > __xen_pgd_walk(mm, pgd, xen_unpin_page, USER_LIMIT);
> >
> > xen_mc_issue(0);
> > + spin_unlock(&hack_lock);
> > }
> >
> > static void xen_pgd_unpin(struct mm_struct *mm)
> > @@ -1521,6 +1525,9 @@ static void xen_pgd_free(struct mm_struct *mm, pgd_t
> > *pgd)
> > static void *xen_kmap_atomic_pte(struct page *page, enum km_type type)
> > {
> > pgprot_t prot = PAGE_KERNEL;
> > + void *ret;
> > +
> > + spin_lock(&hack_lock);
> >
> > if (PagePinned(page))
> > prot = PAGE_KERNEL_RO;
> > @@ -1530,7 +1537,11 @@ static void *xen_kmap_atomic_pte(struct page *page,
> > enum km_type type)
> > page_to_pfn(page), type,
> > (unsigned long)pgprot_val(prot) & _PAGE_RW ? "WRITE" :
> > "READ");
> >
> > - return kmap_atomic_prot(page, type, prot);
> > + ret = kmap_atomic_prot(page, type, prot);
> > +
> > + spin_unlock(&hack_lock);
> > +
> > + return ret;
> > }
> > #endif
> >
> >
> >
>
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