| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <28f82bf0-da91-4330-869e-f41e1559482b@redhat.com>
Date: Mon, 16 Jun 2025 10:28:47 +0200
From: David Hildenbrand <david@...hat.com>
To: lizhe.67@...edance.com, alex.williamson@...hat.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, peterx@...hat.com
Subject: Re: [PATCH v3 2/2] vfio/type1: optimize vfio_unpin_pages_remote() for
large folio
On 16.06.25 10:27, David Hildenbrand wrote:
> On 16.06.25 10:14, David Hildenbrand wrote:
>> On 16.06.25 09:52, lizhe.67@...edance.com wrote:
>>> From: Li Zhe <lizhe.67@...edance.com>
>>>
>>> When vfio_unpin_pages_remote() is called with a range of addresses that
>>> includes large folios, the function currently performs individual
>>> put_pfn() operations for each page. This can lead to significant
>>> performance overheads, especially when dealing with large ranges of pages.
>>>
>>> This patch optimize this process by batching the put_pfn() operations.
>>>
>>> The performance test results, based on v6.15, for completing the 16G VFIO
>>> IOMMU DMA unmapping, obtained through unit test[1] with slight
>>> modifications[2], are as follows.
>>>
>>> Base(v6.15):
>>> ./vfio-pci-mem-dma-map 0000:03:00.0 16
>>> ------- AVERAGE (MADV_HUGEPAGE) --------
>>> VFIO MAP DMA in 0.047 s (338.6 GB/s)
>>> VFIO UNMAP DMA in 0.138 s (116.2 GB/s)
>>> ------- AVERAGE (MAP_POPULATE) --------
>>> VFIO MAP DMA in 0.280 s (57.2 GB/s)
>>> VFIO UNMAP DMA in 0.312 s (51.3 GB/s)
>>> ------- AVERAGE (HUGETLBFS) --------
>>> VFIO MAP DMA in 0.052 s (308.3 GB/s)
>>> VFIO UNMAP DMA in 0.139 s (115.1 GB/s)
>>>
>>> Map[3] + This patchset:
>>> ------- AVERAGE (MADV_HUGEPAGE) --------
>>> VFIO MAP DMA in 0.027 s (598.2 GB/s)
>>> VFIO UNMAP DMA in 0.049 s (328.7 GB/s)
>>> ------- AVERAGE (MAP_POPULATE) --------
>>> VFIO MAP DMA in 0.289 s (55.3 GB/s)
>>> VFIO UNMAP DMA in 0.303 s (52.9 GB/s)
>>> ------- AVERAGE (HUGETLBFS) --------
>>> VFIO MAP DMA in 0.032 s (506.8 GB/s)
>>> VFIO UNMAP DMA in 0.049 s (326.7 GB/s)
>>>
>>> For large folio, we achieve an approximate 64% performance improvement
>>> in the VFIO UNMAP DMA item. For small folios, the performance test
>>> results appear to show no significant changes.
>>>
>>> [1]: https://github.com/awilliam/tests/blob/vfio-pci-mem-dma-map/vfio-pci-mem-dma-map.c
>>> [2]: https://lore.kernel.org/all/20250610031013.98556-1-lizhe.67@bytedance.com/
>>> [3]: https://lore.kernel.org/all/20250529064947.38433-1-lizhe.67@bytedance.com/
>>>
>>> Signed-off-by: Li Zhe <lizhe.67@...edance.com>
>>> ---
>>> drivers/vfio/vfio_iommu_type1.c | 55 +++++++++++++++++++++++++++------
>>> 1 file changed, 46 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>>> index e952bf8bdfab..09ecc546ece8 100644
>>> --- a/drivers/vfio/vfio_iommu_type1.c
>>> +++ b/drivers/vfio/vfio_iommu_type1.c
>>> @@ -469,17 +469,28 @@ static bool is_invalid_reserved_pfn(unsigned long pfn)
>>> return true;
>>> }
>>>
>>> -static int put_pfn(unsigned long pfn, int prot)
>>> +static inline void _put_pfns(struct page *page, int npages, int prot)
>>> {
>>> - if (!is_invalid_reserved_pfn(pfn)) {
>>> - struct page *page = pfn_to_page(pfn);
>>> + unpin_user_page_range_dirty_lock(page, npages, prot & IOMMU_WRITE);
>>> +}
>>>
>>> - unpin_user_pages_dirty_lock(&page, 1, prot & IOMMU_WRITE);
>>> - return 1;
>>> +/*
>>> + * The caller must ensure that these npages PFNs belong to the same folio.
>>> + */
>>> +static inline int put_pfns(unsigned long pfn, int npages, int prot)
>>> +{
>>> + if (!is_invalid_reserved_pfn(pfn)) {
>>> + _put_pfns(pfn_to_page(pfn), npages, prot);
>>> + return npages;
>>> }
>>> return 0;
>>> }
>>>
>>> +static inline int put_pfn(unsigned long pfn, int prot)
>>> +{
>>> + return put_pfns(pfn, 1, prot);
>>> +}
>>> +
>>> #define VFIO_BATCH_MAX_CAPACITY (PAGE_SIZE / sizeof(struct page *))
>>>
>>> static void __vfio_batch_init(struct vfio_batch *batch, bool single)
>>> @@ -806,11 +817,37 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, dma_addr_t iova,
>>> bool do_accounting)
>>> {
>>> long unlocked = 0, locked = vpfn_pages(dma, iova, npage);
>>> - long i;
>>>
>>> - for (i = 0; i < npage; i++)
>>> - if (put_pfn(pfn++, dma->prot))
>>> - unlocked++;
>>> + while (npage) {
>>> + long nr_pages = 1;
>>> +
>>> + if (!is_invalid_reserved_pfn(pfn)) {
>>> + struct page *page = pfn_to_page(pfn);
>>> + struct folio *folio = page_folio(page);
>>> + long folio_pages_num = folio_nr_pages(folio);
>>> +
>>> + /*
>>> + * For a folio, it represents a physically
>>> + * contiguous set of bytes, and all of its pages
>>> + * share the same invalid/reserved state.
>>> + *
>>> + * Here, our PFNs are contiguous. Therefore, if we
>>> + * detect that the current PFN belongs to a large
>>> + * folio, we can batch the operations for the next
>>> + * nr_pages PFNs.
>>> + */
>>> + if (folio_pages_num > 1)
>>> + nr_pages = min_t(long, npage,
>>> + folio_pages_num -
>>> + folio_page_idx(folio, page));
>>> +
>>> + _put_pfns(page, nr_pages, dma->prot);
>>
>>
>> This is sneaky. You interpret the page pointer a an actual page array,
>> assuming that it would give you the right values when advancing nr_pages
>> in that array.
>
> Just to add to this: unpin_user_page_range_dirty_lock() is not
> universally save in the hugetlb scenario I described.
Correction: it is, because gup_folio_range_next() uses "nth_page".
So this should work.
--
Cheers,
David / dhildenb
Powered by blists - more mailing lists