On 4/4/19 1:56 AM, Peter Zijlstra wrote: > On Wed, Apr 03, 2019 at 11:34:12AM -0600, Khalid Aziz wrote: >> From: Julian Stecklina <[email protected]> >> >> Only the xpfo_kunmap call that needs to actually unmap the page >> needs to be serialized. We need to be careful to handle the case, >> where after the atomic decrement of the mapcount, a xpfo_kmap >> increased the mapcount again. In this case, we can safely skip >> modifying the page table. >> >> Model-checked with up to 4 concurrent callers with Spin. >> >> Signed-off-by: Julian Stecklina <[email protected]> >> Signed-off-by: Khalid Aziz <[email protected]> >> Cc: Khalid Aziz <[email protected]> >> Cc: [email protected] >> Cc: [email protected] >> Cc: Vasileios P. Kemerlis <[email protected]> >> Cc: Juerg Haefliger <[email protected]> >> Cc: Tycho Andersen <[email protected]> >> Cc: Marco Benatto <[email protected]> >> Cc: David Woodhouse <[email protected]> >> --- >> include/linux/xpfo.h | 24 +++++++++++++++--------- >> 1 file changed, 15 insertions(+), 9 deletions(-) >> >> diff --git a/include/linux/xpfo.h b/include/linux/xpfo.h >> index 2318c7eb5fb7..37e7f52fa6ce 100644 >> --- a/include/linux/xpfo.h >> +++ b/include/linux/xpfo.h >> @@ -61,6 +61,7 @@ static inline void xpfo_kmap(void *kaddr, struct page >> *page) >> static inline void xpfo_kunmap(void *kaddr, struct page *page) >> { >> unsigned long flags; >> + bool flush_tlb = false; >> >> if (!static_branch_unlikely(&xpfo_inited)) >> return; >> @@ -72,18 +73,23 @@ static inline void xpfo_kunmap(void *kaddr, struct page >> *page) >> * The page is to be allocated back to user space, so unmap it from >> * the kernel, flush the TLB and tag it as a user page. >> */ >> - spin_lock_irqsave(&page->xpfo_lock, flags); >> - >> if (atomic_dec_return(&page->xpfo_mapcount) == 0) { >> -#ifdef CONFIG_XPFO_DEBUG >> - WARN_ON(PageXpfoUnmapped(page)); >> -#endif >> - SetPageXpfoUnmapped(page); >> - set_kpte(kaddr, page, __pgprot(0)); >> - xpfo_flush_kernel_tlb(page, 0); >> + spin_lock_irqsave(&page->xpfo_lock, flags); >> + >> + /* >> + * In the case, where we raced with kmap after the >> + * atomic_dec_return, we must not nuke the mapping. >> + */ >> + if (atomic_read(&page->xpfo_mapcount) == 0) { >> + SetPageXpfoUnmapped(page); >> + set_kpte(kaddr, page, __pgprot(0)); >> + flush_tlb = true; >> + } >> + spin_unlock_irqrestore(&page->xpfo_lock, flags); >> } >> >> - spin_unlock_irqrestore(&page->xpfo_lock, flags); >> + if (flush_tlb) >> + xpfo_flush_kernel_tlb(page, 0); >> } > > This doesn't help with the TLB invalidation issue, AFAICT this is still > completely buggered. kunmap_atomic() can be called from IRQ context. >
OK. xpfo_kmap/xpfo_kunmap need redesign. -- Khalid _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
