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Message-ID: <1bd50178755535ee0a3b0b2164acf9319079a3d5.camel@linux.ibm.com>
Date: Tue, 22 Jul 2025 12:32:59 -0400
From: Eric Farman <farman@...ux.ibm.com>
To: lizhe.67@...edance.com, alex.williamson@...hat.com,
akpm@...ux-foundation.org, david@...hat.com, jgg@...pe.ca,
peterx@...hat.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 2/5] vfio/type1: optimize vfio_pin_pages_remote()
On Thu, 2025-07-10 at 16:53 +0800, lizhe.67@...edance.com wrote:
> From: Li Zhe <lizhe.67@...edance.com>
>
> When vfio_pin_pages_remote() is called with a range of addresses that
> includes large folios, the function currently performs individual
> statistics counting operations for each page. This can lead to significant
> performance overheads, especially when dealing with large ranges of pages.
> Batch processing of statistical counting operations can effectively enhance
> performance.
>
> In addition, the pages obtained through longterm GUP are neither invalid
> nor reserved. Therefore, we can reduce the overhead associated with some
> calls to function is_invalid_reserved_pfn().
>
> The performance test results for completing the 16G VFIO IOMMU DMA mapping
> are as follows.
>
> Base(v6.16-rc4):
> ------- AVERAGE (MADV_HUGEPAGE) --------
> VFIO MAP DMA in 0.047 s (340.2 GB/s)
> ------- AVERAGE (MAP_POPULATE) --------
> VFIO MAP DMA in 0.280 s (57.2 GB/s)
> ------- AVERAGE (HUGETLBFS) --------
> VFIO MAP DMA in 0.052 s (310.5 GB/s)
>
> With this patch:
> ------- AVERAGE (MADV_HUGEPAGE) --------
> VFIO MAP DMA in 0.027 s (602.1 GB/s)
> ------- AVERAGE (MAP_POPULATE) --------
> VFIO MAP DMA in 0.257 s (62.4 GB/s)
> ------- AVERAGE (HUGETLBFS) --------
> VFIO MAP DMA in 0.031 s (517.4 GB/s)
>
> For large folio, we achieve an over 40% performance improvement.
> For small folios, the performance test results indicate a
> slight improvement.
>
> Signed-off-by: Li Zhe <lizhe.67@...edance.com>
> Co-developed-by: Alex Williamson <alex.williamson@...hat.com>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 83 ++++++++++++++++++++++++++++-----
> 1 file changed, 71 insertions(+), 12 deletions(-)
Hi,
Our CI started flagging some crashes running vfio-ccw regressions on the -next kernel beginning with
next-20250717, and bisect points to this particular commit.
I can reproduce by cherry-picking this series onto 6.16-rc7, so it's not something else lurking.
Without panic_on_warn, I get a handful of warnings from vfio_remove_dma() (after starting/stopping
guests with an mdev attached), before eventually triggering a BUG() in vfio_dma_do_unmap() running a
hotplug test. I've attached an example of a WARNING before the eventual BUG below. I can help debug
this if more doc is needed, but admit I haven't looked at this patch in any detail yet.
Thanks,
Eric
[ 215.671885] ------------[ cut here ]------------
[ 215.671893] WARNING: CPU: 10 PID: 6210 at drivers/vfio/vfio_iommu_type1.c:1204
vfio_remove_dma+0xda/0xf0 [vfio_iommu_type1]
[ 215.671902] Modules linked in: vhost_vsock vmw_vsock_virtio_transport_common vsock vhost
vhost_iotlb algif_hash af_alg kvm nft_masq nft_ct nft_reject_ipv4 nf_reject_ipv4 nft_reject act_csum
cls_u32 sch_htb nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables pkey_pckmo
s390_trng pkey_ep11 pkey_cca zcrypt_cex4 zcrypt eadm_sch rng_core vfio_ccw mdev vfio_iommu_type1
vfio drm sch_fq_codel i2c_core drm_panel_orientation_quirks dm_multipath loop nfnetlink ctcm fsm
zfcp scsi_transport_fc mlx5_ib diag288_wdt mlx5_core ghash_s390 prng aes_s390 des_s390 libdes
sha3_512_s390 sha3_256_s390 sha512_s390 sha1_s390 sha_common rpcrdma sunrpc rdma_ucm rdma_cm
configfs iw_cm ib_cm ib_uverbs ib_core scsi_dh_rdac scsi_dh_emc scsi_dh_alua pkey autofs4
[ 215.671946] CPU: 10 UID: 107 PID: 6210 Comm: qemu-system-s39 Kdump: loaded Not tainted 6.16.0-
rc7-00005-g4ff8295d8d61 #79 NONE
[ 215.671950] Hardware name: IBM 3906 M05 780 (LPAR)
[ 215.671951] Krnl PSW : 0704c00180000000 000002482f7ee55e (vfio_remove_dma+0xde/0xf0
[vfio_iommu_type1])
[ 215.671956] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
[ 215.671959] Krnl GPRS: 006d010100000000 000000009d8a4c40 000000008f3b1c80 0000000092ffad20
[ 215.671961] 0000000090b57880 006e010100000000 000000008f3b1c80 000000008f3b1cc8
[ 215.671963] 0000000085b3ff00 000000008f3b1cc0 000000008f3b1c80 0000000092ffad20
[ 215.671964] 000003ff867acfa8 000000008f3b1ca0 000001c8b36c3be0 000001c8b36c3ba8
[ 215.671972] Krnl Code: 000002482f7ee550: c0e53ff9fcc8 brasl %r14,00000248af72dee0
000002482f7ee556: a7f4ffcf brc 15,000002482f7ee4f4
#000002482f7ee55a: af000000 mc 0,0
>000002482f7ee55e: a7f4ffa9 brc 15,000002482f7ee4b0
000002482f7ee562: 0707 bcr 0,%r7
000002482f7ee564: 0707 bcr 0,%r7
000002482f7ee566: 0707 bcr 0,%r7
000002482f7ee568: 0707 bcr 0,%r7
[ 215.672006] Call Trace:
[ 215.672008] [<000002482f7ee55e>] vfio_remove_dma+0xde/0xf0 [vfio_iommu_type1]
[ 215.672013] [<000002482f7f03de>] vfio_iommu_type1_detach_group+0x3de/0x5f0 [vfio_iommu_type1]
[ 215.672016] [<000002482f7d4c4e>] vfio_group_detach_container+0x5e/0x180 [vfio]
[ 215.672023] [<000002482f7d2ce0>] vfio_group_fops_release+0x50/0x90 [vfio]
[ 215.672027] [<00000248af25e1ee>] __fput+0xee/0x2e0
[ 215.672031] [<00000248aef19f18>] task_work_run+0x88/0xd0
[ 215.672036] [<00000248aeef559a>] do_exit+0x18a/0x4e0
[ 215.672042] [<00000248aeef5ab0>] do_group_exit+0x40/0xc0
[ 215.672045] [<00000248aeef5b5e>] __s390x_sys_exit_group+0x2e/0x30
[ 215.672048] [<00000248afc81e56>] __do_syscall+0x136/0x340
[ 215.672054] [<00000248afc8da7e>] system_call+0x6e/0x90
[ 215.672058] Last Breaking-Event-Address:
[ 215.672059] [<000002482f7ee4aa>] vfio_remove_dma+0x2a/0xf0 [vfio_iommu_type1]
[ 215.672062] ---[ end trace 0000000000000000 ]---
[ 219.861940] ------------[ cut here ]------------
...
[ 241.164333] ------------[ cut here ]------------
[ 241.164340] kernel BUG at drivers/vfio/vfio_iommu_type1.c:1480!
[ 241.164358] monitor event: 0040 ilc:2 [#1]SMP
[ 241.164363] Modules linked in: vhost_vsock vmw_vsock_virtio_transport_common vsock vhost
vhost_iotlb algif_hash af_alg kvm nft_masq nft_ct nft_reject_ipv4 nf_reject_ipv4 nft_reject act_csum
cls_u32 sch_htb nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables pkey_pckmo
s390_trng pkey_ep11 pkey_cca zcrypt_cex4 zcrypt eadm_sch rng_core vfio_ccw mdev vfio_iommu_type1
vfio drm sch_fq_codel i2c_core drm_panel_orientation_quirks dm_multipath loop nfnetlink ctcm fsm
zfcp scsi_transport_fc mlx5_ib diag288_wdt mlx5_core ghash_s390 prng aes_s390 des_s390 libdes
sha3_512_s390 sha3_256_s390 sha512_s390 sha1_s390 sha_common rpcrdma sunrpc rdma_ucm rdma_cm
configfs iw_cm ib_cm ib_uverbs ib_core scsi_dh_rdac scsi_dh_emc scsi_dh_alua pkey autofs4
[ 241.164399] CPU: 14 UID: 107 PID: 6581 Comm: qemu-system-s39 Kdump: loaded Tainted: G W
6.16.0-rc7-00005-g4ff8295d8d61 #79 NONE
[ 241.164403] Tainted: [W]=WARN
[ 241.164404] Hardware name: IBM 3906 M05 780 (LPAR)
[ 241.164406] Krnl PSW : 0704e00180000000 000002482f7f132a (vfio_dma_do_unmap+0x4aa/0x4b0
[vfio_iommu_type1])
[ 241.164413] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
[ 241.164415] Krnl GPRS: 0000000000000000 000000000000000b 0000000040000000 000000008cfdcb40
[ 241.164418] 0000000000001001 0000000000000001 0000000000000000 0000000040000000
[ 241.164419] 0000000000000000 0000000000000000 00000001fbe7f140 000000008cfdcb40
[ 241.164421] 000003ff97dacfa8 0000000000000000 00000000871582c0 000001c8b4177cd0
[ 241.164428] Krnl Code: 000002482f7f131e: a7890000 lghi %r8,0
000002482f7f1322: a7f4feeb brc 15,000002482f7f10f8
#000002482f7f1326: af000000 mc 0,0
>000002482f7f132a: 0707 bcr 0,%r7
000002482f7f132c: 0707 bcr 0,%r7
000002482f7f132e: 0707 bcr 0,%r7
000002482f7f1330: c0040000803c brcl 0,000002482f8013a8
000002482f7f1336: eb6ff0480024 stmg %r6,%r15,72(%r15)
[ 241.164458] Call Trace:
[ 241.164459] [<000002482f7f132a>] vfio_dma_do_unmap+0x4aa/0x4b0 [vfio_iommu_type1]
[ 241.164463] [<000002482f7f1d08>] vfio_iommu_type1_ioctl+0x1c8/0x370 [vfio_iommu_type1]
[ 241.164466] [<00000248af27704e>] vfs_ioctl+0x2e/0x70
[ 241.164471] [<00000248af278610>] __s390x_sys_ioctl+0xe0/0x100
[ 241.164474] [<00000248afc81e56>] __do_syscall+0x136/0x340
[ 241.164477] [<00000248afc8da7e>] system_call+0x6e/0x90
[ 241.164481] Last Breaking-Event-Address:
[ 241.164482] [<000002482f7f1238>] vfio_dma_do_unmap+0x3b8/0x4b0 [vfio_iommu_type1]
[ 241.164486] Kernel panic - not syncing: Fatal exception: panic_on_oops
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 1136d7ac6b59..6909275e46c2 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -318,7 +318,13 @@ static void vfio_dma_bitmap_free_all(struct vfio_iommu *iommu)
> /*
> * Helper Functions for host iova-pfn list
> */
> -static struct vfio_pfn *vfio_find_vpfn(struct vfio_dma *dma, dma_addr_t iova)
> +
> +/*
> + * Find the highest vfio_pfn that overlapping the range
> + * [iova_start, iova_end) in rb tree.
> + */
> +static struct vfio_pfn *vfio_find_vpfn_range(struct vfio_dma *dma,
> + dma_addr_t iova_start, dma_addr_t iova_end)
> {
> struct vfio_pfn *vpfn;
> struct rb_node *node = dma->pfn_list.rb_node;
> @@ -326,9 +332,9 @@ static struct vfio_pfn *vfio_find_vpfn(struct vfio_dma *dma, dma_addr_t iova)
> while (node) {
> vpfn = rb_entry(node, struct vfio_pfn, node);
>
> - if (iova < vpfn->iova)
> + if (iova_end <= vpfn->iova)
> node = node->rb_left;
> - else if (iova > vpfn->iova)
> + else if (iova_start > vpfn->iova)
> node = node->rb_right;
> else
> return vpfn;
> @@ -336,6 +342,11 @@ static struct vfio_pfn *vfio_find_vpfn(struct vfio_dma *dma, dma_addr_t iova)
> return NULL;
> }
>
> +static inline struct vfio_pfn *vfio_find_vpfn(struct vfio_dma *dma, dma_addr_t iova)
> +{
> + return vfio_find_vpfn_range(dma, iova, iova + PAGE_SIZE);
> +}
> +
> static void vfio_link_pfn(struct vfio_dma *dma,
> struct vfio_pfn *new)
> {
> @@ -614,6 +625,39 @@ static long vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
> return ret;
> }
>
> +
> +static long vpfn_pages(struct vfio_dma *dma,
> + dma_addr_t iova_start, long nr_pages)
> +{
> + dma_addr_t iova_end = iova_start + (nr_pages << PAGE_SHIFT);
> + struct vfio_pfn *top = vfio_find_vpfn_range(dma, iova_start, iova_end);
> + long ret = 1;
> + struct vfio_pfn *vpfn;
> + struct rb_node *prev;
> + struct rb_node *next;
> +
> + if (likely(!top))
> + return 0;
> +
> + prev = next = &top->node;
> +
> + while ((prev = rb_prev(prev))) {
> + vpfn = rb_entry(prev, struct vfio_pfn, node);
> + if (vpfn->iova < iova_start)
> + break;
> + ret++;
> + }
> +
> + while ((next = rb_next(next))) {
> + vpfn = rb_entry(next, struct vfio_pfn, node);
> + if (vpfn->iova >= iova_end)
> + break;
> + ret++;
> + }
> +
> + return ret;
> +}
> +
> /*
> * Attempt to pin pages. We really don't want to track all the pfns and
> * the iommu can only map chunks of consecutive pfns anyway, so get the
> @@ -680,32 +724,47 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
> * and rsvd here, and therefore continues to use the batch.
> */
> while (true) {
> + long nr_pages, acct_pages = 0;
> +
> if (pfn != *pfn_base + pinned ||
> rsvd != is_invalid_reserved_pfn(pfn))
> goto out;
>
> + /*
> + * Using GUP with the FOLL_LONGTERM in
> + * vaddr_get_pfns() will not return invalid
> + * or reserved pages.
> + */
> + nr_pages = num_pages_contiguous(
> + &batch->pages[batch->offset],
> + batch->size);
> + if (!rsvd) {
> + acct_pages = nr_pages;
> + acct_pages -= vpfn_pages(dma, iova, nr_pages);
> + }
> +
> /*
> * Reserved pages aren't counted against the user,
> * externally pinned pages are already counted against
> * the user.
> */
> - if (!rsvd && !vfio_find_vpfn(dma, iova)) {
> + if (acct_pages) {
> if (!dma->lock_cap &&
> - mm->locked_vm + lock_acct + 1 > limit) {
> + mm->locked_vm + lock_acct + acct_pages > limit) {
> pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
> __func__, limit << PAGE_SHIFT);
> ret = -ENOMEM;
> goto unpin_out;
> }
> - lock_acct++;
> + lock_acct += acct_pages;
> }
>
> - pinned++;
> - npage--;
> - vaddr += PAGE_SIZE;
> - iova += PAGE_SIZE;
> - batch->offset++;
> - batch->size--;
> + pinned += nr_pages;
> + npage -= nr_pages;
> + vaddr += PAGE_SIZE * nr_pages;
> + iova += PAGE_SIZE * nr_pages;
> + batch->offset += nr_pages;
> + batch->size -= nr_pages;
>
> if (!batch->size)
> break;
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