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Message-ID: <f22a8b5b50a140339222bed77f4b670d9008f29b.camel@linux.ibm.com>
Date: Wed, 23 Jul 2025 10:41:34 -0400
From: Eric Farman <farman@...ux.ibm.com>
To: lizhe.67@...edance.com
Cc: akpm@...ux-foundation.org, alex.williamson@...hat.com, david@...hat.com,
jgg@...pe.ca, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, peterx@...hat.com
Subject: Re: [PATCH v4 2/5] vfio/type1: optimize vfio_pin_pages_remote()
On Wed, 2025-07-23 at 15:09 +0800, lizhe.67@...edance.com wrote:
> On Tue, 22 Jul 2025 12:32:59 -0400, farman@...ux.ibm.com wrote:
>
> > 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
>
> Thanks for the report. After a review of this commit, it appears that
> only the changes to vfio_find_vpfn() could plausibly account for the
> observed issue (I cannot be absolutely certain). Could you kindly test
> whether the issue persists after applying the following patch?
Hi Zhe,
Thank you for the quick patch! I applied this and ran through a few cycles of the previously-
problematic tests, and things are holding up great.
It's probably a fixup to the commit here, but FWIW:
Tested-by: Eric Farman <farman@...ux.ibm.com>
Thanks,
Eric
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -344,7 +344,7 @@ static struct vfio_pfn *vfio_find_vpfn_range(struct vfio_dma *dma,
>
> 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);
> + return vfio_find_vpfn_range(dma, iova, iova + 1);
> }
>
> Thanks,
> Zhe
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