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Date: Wed, 24 Jul 2013 09:25:19 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: dwmw2@...radead.org
Cc: 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
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);
>
--
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