Re: [PATCH] iommufd/selftest: Don't check map/unmap pairing with HUGE_PAGES

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Feb 23, 2024 at 02:44:08PM -0400, Jason Gunthorpe wrote:
> Since MOCK_HUGE_PAGE_SIZE was introduced it allows the core code to invoke
> mock with large page sizes. This confuses the validation logic that checks
> that map/unmap are paired.
> 
> This is because the page size computed for map is based on the physical
> address and in many cases will always be the base page size, however the
> entire range generated by iommufd will be be passed to map.
> 
> Randomly iommufd can see small groups of physically contiguous pages,
> (say 8k aligned and grouped together), but that group crosses a huge page
> boundary. The map side will observe this as a contiguous run and mark it
> accordingly, but there is a chance the unmap side will end up terminating
> interior huge pages in the middle of that group and trigger a validation
> failure. Meaning the validation only works if the core code passes the
> iova/length directly from iommufd to mock.
> 
> syzkaller randomly hits this with failures like:
> 
>   WARNING: CPU: 0 PID: 11568 at drivers/iommu/iommufd/selftest.c:461 mock_domain_unmap_pages+0x1c0/0x250
>   Modules linked in:
>   CPU: 0 PID: 11568 Comm: syz-executor.0 Not tainted 6.8.0-rc3+ #4
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
>   RIP: 0010:mock_domain_unmap_pages+0x1c0/0x250
>   Code: 2b e8 94 37 0f ff 48 d1 eb 31 ff 48 b8 00 00 00 00 00 00 20 00 48 21 c3 48 89 de e8 aa 32 0f ff 48 85 db 75 07 e8 70 37 0f ff <0f> 0b e8 69 37 0f ff 31 f6 31 ff e8 90 32 0f ff e8 5b 37 0f ff 4c
>   RSP: 0018:ffff88800e707490 EFLAGS: 00010293
>   RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff822dfae6
>   RDX: ffff88800cf86400 RSI: ffffffff822dfaf0 RDI: 0000000000000007
>   RBP: ffff88800e7074d8 R08: 0000000000000000 R09: ffffed1001167c90
>   R10: 0000000000000000 R11: 0000000000000000 R12: 0000000001500000
>   R13: 0000000000083000 R14: 0000000000000001 R15: 0000000000000800
>   FS:  0000555556048480(0000) GS:ffff88806d400000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 0000001b2dc23000 CR3: 0000000008cbb000 CR4: 0000000000350eb0
>   Call Trace:
>    <TASK>
>    __iommu_unmap+0x281/0x520
>    iommu_unmap+0xc9/0x180
>    iopt_area_unmap_domain_range+0x1b1/0x290
>    iopt_area_unpin_domain+0x590/0x800
>    __iopt_area_unfill_domain+0x22e/0x650
>    iopt_area_unfill_domain+0x47/0x60
>    iopt_unfill_domain+0x187/0x590
>    iopt_table_remove_domain+0x267/0x2d0
>    iommufd_hwpt_paging_destroy+0x1f1/0x370
>    iommufd_object_remove+0x2a3/0x490
>    iommufd_device_detach+0x23a/0x2c0
>    iommufd_selftest_destroy+0x7a/0xf0
>    iommufd_fops_release+0x1d3/0x340
>    __fput+0x272/0xb50
>    __fput_sync+0x4b/0x60
>    __x64_sys_close+0x8b/0x110
>    do_syscall_64+0x71/0x140
>    entry_SYSCALL_64_after_hwframe+0x46/0x4e
> 
> Do the simple thing and just disable the validation when the huge page
> tests are being run.
> 
> Fixes: 7db521e23fe9 ("iommufd/selftest: Hugepage mock domain support")
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  drivers/iommu/iommufd/selftest.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)

Applied to for-rc, thanks

Jason