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Date: Tue, 6 Aug 2013 13:08:42 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: dwmw2@...radead.org, iommu@...ts.linux-foundation.org,
ddutile@...hat.com, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org
Subject: Re: [PATCH] intel-iommu: Fix leaks in pagetable freeing
On Wed, Jul 24, 2013 at 09:25:19AM -0600, Alex Williamson wrote:
>
> This is a pretty massive memory leak, anyone @Intel care? Thanks,
>
> Alex
>
> On Sat, 2013-06-15 at 10:27 -0600, Alex Williamson wrote:
> > At best the current code only seems to free the leaf pagetables and
> > the root. If you're unlucky enough to have a large gap (like any
> > QEMU guest with more than 3G of memory), only the first chunk of leaf
> > pagetables are freed (plus the root). This is a massive memory leak.
> > This patch re-writes the pagetable freeing function to use a
> > recursive algorithm and manages to not only free all the pagetables,
> > but does it without any apparent performance loss versus the current
> > broken version.
> >
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> > Cc: stable@...r.kernel.org
> > ---
> >
> > Suggesting for stable, would like to see some soak time, but it's
> > hard to imagine this being any worse than the current code.
> >
> > This likely also affects device domains, but the current code does
> > ok at freeing individual leaf pagetables and driver domains would
> > only get a full pruning if the driver or device is removed.
> >
> > Some test programs:
> > https://github.com/awilliam/tests/blob/master/kvm-huge-guest-test.c
> > https://github.com/awilliam/tests/blob/master/vfio-huge-guest-test.c
> >
> > Both of these simulate a large guest on a small host system. They
> > mmap 4G of memory and map it across a large address space just like
> > QEMU would (aside from re-using the same mmap across multiple IOVAs).
> > On existing code the vfio version (w/o a KVM memory slot limit) will
> > leak over 1G of pagetables per run.
> >
> > drivers/iommu/intel-iommu.c | 72 +++++++++++++++++++++----------------------
> > 1 file changed, 35 insertions(+), 37 deletions(-)
> >
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index eec0d3e..15e9b57 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -890,56 +890,54 @@ static int dma_pte_clear_range(struct dmar_domain *domain,
> > return order;
> > }
> >
> > +static void dma_pte_free_level(struct dmar_domain *domain, int level,
> > + struct dma_pte *pte, unsigned long pfn,
> > + unsigned long start_pfn, unsigned long last_pfn)
> > +{
> > + pfn = max(start_pfn, pfn);
> > + pte = &pte[pfn_level_offset(pfn, level)];
> > +
> > + do {
> > + unsigned long level_pfn;
> > + struct dma_pte *level_pte;
> > +
> > + if (!dma_pte_present(pte) || dma_pte_superpage(pte))
> > + goto next;
> > +
> > + level_pfn = pfn & level_mask(level - 1);
> > + level_pte = phys_to_virt(dma_pte_addr(pte));
> > +
> > + if (level > 2)
> > + dma_pte_free_level(domain, level - 1, level_pte,
> > + level_pfn, start_pfn, last_pfn);
> > +
> > + /* If range covers entire pagetable, free it */
> > + if (!(start_pfn > level_pfn ||
> > + last_pfn < level_pfn + level_size(level))) {
> > + dma_clear_pte(pte);
> > + domain_flush_cache(domain, pte, sizeof(*pte));
> > + free_pgtable_page(level_pte);
> > + }
> > +next:
> > + pfn += level_size(level);
> > + } while (!first_pte_in_page(++pte) && pfn <= last_pfn);
> > +}
> > +
> > /* free page table pages. last level pte should already be cleared */
> > static void dma_pte_free_pagetable(struct dmar_domain *domain,
> > unsigned long start_pfn,
> > unsigned long last_pfn)
> > {
> > int addr_width = agaw_to_width(domain->agaw) - VTD_PAGE_SHIFT;
> > - struct dma_pte *first_pte, *pte;
> > - int total = agaw_to_level(domain->agaw);
> > - int level;
> > - unsigned long tmp;
> > - int large_page = 2;
> >
> > BUG_ON(addr_width < BITS_PER_LONG && start_pfn >> addr_width);
> > BUG_ON(addr_width < BITS_PER_LONG && last_pfn >> addr_width);
> > BUG_ON(start_pfn > last_pfn);
> >
> > /* We don't need lock here; nobody else touches the iova range */
> > - level = 2;
> > - while (level <= total) {
> > - tmp = align_to_level(start_pfn, level);
> > -
> > - /* If we can't even clear one PTE at this level, we're done */
> > - if (tmp + level_size(level) - 1 > last_pfn)
> > - return;
> > -
> > - do {
> > - large_page = level;
> > - first_pte = pte = dma_pfn_level_pte(domain, tmp, level, &large_page);
> > - if (large_page > level)
> > - level = large_page + 1;
> > - if (!pte) {
> > - tmp = align_to_level(tmp + 1, level + 1);
> > - continue;
> > - }
> > - do {
> > - if (dma_pte_present(pte)) {
> > - free_pgtable_page(phys_to_virt(dma_pte_addr(pte)));
> > - dma_clear_pte(pte);
> > - }
> > - pte++;
> > - tmp += level_size(level);
> > - } while (!first_pte_in_page(pte) &&
> > - tmp + level_size(level) - 1 <= last_pfn);
> > + dma_pte_free_level(domain, agaw_to_level(domain->agaw),
> > + domain->pgd, 0, start_pfn, last_pfn);
> >
> > - domain_flush_cache(domain, first_pte,
> > - (void *)pte - (void *)first_pte);
> > -
> > - } while (tmp && tmp + level_size(level) - 1 <= last_pfn);
> > - level++;
> > - }
> > /* free pgd */
> > if (start_pfn == 0 && last_pfn == DOMAIN_MAX_PFN(domain->gaw)) {
> > free_pgtable_page(domain->pgd);
> >
Reviewed-by: Marcelo Tosatti <mtosatti@...hat.com>
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