Re: [PATCH] iommu/vt-d: Fix panic after kexec -p for kdump

[Lu Baolu]

Hi John,

On 10/18/19 10:17 PM, John Donnelly wrote:
> This cures a panic on restart after a kexec -p  operation on 5.3 and 5.4 kernels.
>
> The underlying state of the iommu registers (iommu->flags &
> VTD_FLAG_TRANS_PRE_ENABLED) on a restart results in a domain being marked as
> "DEFER_DEVICE_DOMAIN_INFO" that produces an Oops in identity_mapping().
>
> [   43.654737] BUG: kernel NULL pointer dereference, address:
> 0000000000000056
> [   43.655720] #PF: supervisor read access in kernel mode
> [   43.655720] #PF: error_code(0x0000) - not-present page
> [   43.655720] PGD 0 P4D 0
> [   43.655720] Oops: 0000 [#1] SMP PTI
> [   43.655720] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
> 5.3.2-1940.el8uek.x86_64 #1
> [   43.655720] Hardware name: Oracle Corporation ORACLE SERVER
> X5-2/ASM,MOTHERBOARD,1U, BIOS 30140300 09/20/2018
> [   43.655720] RIP: 0010:iommu_need_mapping+0x29/0xd0
> [   43.655720] Code: 00 0f 1f 44 00 00 48 8b 97 70 02 00 00 48 83 fa ff
> 74 53 48 8d 4a ff b8 01 00 00 00 48 83 f9 fd 76 01 c3 48 8b 35 7f 58 e0
> 01 <48> 39 72 58 75 f2 55 48 89 e5 41 54 53 48 8b 87 28 02 00 00 4c 8b
> [   43.655720] RSP: 0018:ffffc9000001b9b0 EFLAGS: 00010246
> [   43.655720] RAX: 0000000000000001 RBX: 0000000000001000 RCX:
> fffffffffffffffd
> [   43.655720] RDX: fffffffffffffffe RSI: ffff8880719b8000 RDI:
> ffff8880477460b0
> [   43.655720] RBP: ffffc9000001b9e8 R08: 0000000000000000 R09:
> ffff888047c01700
> [   43.655720] R10: 00002194036fc692 R11: 0000000000000000 R12:
> 0000000000000000
> [   43.655720] R13: ffff8880477460b0 R14: 0000000000000cc0 R15:
> ffff888072d2b558
> [   43.655720] FS:  0000000000000000(0000) GS:ffff888071c00000(0000)
> knlGS:0000000000000000
> [   43.655720] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   43.655720] CR2: 0000000000000056 CR3: 000000007440a002 CR4:
> 00000000001606b0
> [   43.655720] Call Trace:
> [   43.655720]  ? intel_alloc_coherent+0x2a/0x180
> [   43.655720]  ? __schedule+0x2c2/0x650
> [   43.655720]  dma_alloc_attrs+0x8c/0xd0
> [   43.655720]  dma_pool_alloc+0xdf/0x200
> [   43.655720]  ehci_qh_alloc+0x58/0x130
> [   43.655720]  ehci_setup+0x287/0x7ba
> [   43.655720]  ? _dev_info+0x6c/0x83
> [   43.655720]  ehci_pci_setup+0x91/0x436
> [   43.655720]  usb_add_hcd.cold.48+0x1d4/0x754
> [   43.655720]  usb_hcd_pci_probe+0x2bc/0x3f0
> [   43.655720]  ehci_pci_probe+0x39/0x40
> [   43.655720]  local_pci_probe+0x47/0x80
> [   43.655720]  pci_device_probe+0xff/0x1b0
> [   43.655720]  really_probe+0xf5/0x3a0
> [   43.655720]  driver_probe_device+0xbb/0x100
> [   43.655720]  device_driver_attach+0x58/0x60
> [   43.655720]  __driver_attach+0x8f/0x150
> [   43.655720]  ? device_driver_attach+0x60/0x60
> [   43.655720]  bus_for_each_dev+0x74/0xb0
> [   43.655720]  driver_attach+0x1e/0x20
> [   43.655720]  bus_add_driver+0x151/0x1f0
> [   43.655720]  ? ehci_hcd_init+0xb2/0xb2
> [   43.655720]  ? do_early_param+0x95/0x95
> [   43.655720]  driver_register+0x70/0xc0
> [   43.655720]  ? ehci_hcd_init+0xb2/0xb2
> [   43.655720]  __pci_register_driver+0x57/0x60
> [   43.655720]  ehci_pci_init+0x6a/0x6c
> [   43.655720]  do_one_initcall+0x4a/0x1fa
> [   43.655720]  ? do_early_param+0x95/0x95
> [   43.655720]  kernel_init_freeable+0x1bd/0x262
> [   43.655720]  ? rest_init+0xb0/0xb0
> [   43.655720]  kernel_init+0xe/0x110
> [   43.655720]  ret_from_fork+0x24/0x50

Good catch. Can you please add:

Fixes: 8af46c784ecfe ("iommu/vt-d: Implement is_attach_deferred iommu 
ops entry")
Cc: stable@xxxxxxxxxxxxxxx # v5.3+

With above:

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

Best regards,
Baolu

> Signed-off-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
> ---
> drivers/iommu/intel-iommu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index c4e0e4a9ee9e..f83a9a302f8e 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2783,7 +2783,7 @@ static int identity_mapping(struct device *dev)
> 	struct device_domain_info *info;
>
> 	info = dev->archdata.iommu;
> -	if (info && info != DUMMY_DEVICE_DOMAIN_INFO)
> +	if (info && info != DUMMY_DEVICE_DOMAIN_INFO && info != DEFER_DEVICE_DOMAIN_INFO)
> 		return (info->domain == si_domain);
>
> 	return 0;