Re: [Xen-devel] [PATCH v3 2/2] libxl: don't reset device when it is accessible by the guest

[Wei Liu <wei.liu2@xxxxxxxxxx>]

Where is 1/2 in this series?

On Tue, Dec 18, 2018 at 10:43:38PM +0800, Chao Gao wrote:
> When I destroyed a guest with 'xl destroy', I found the warning
> in msi_set_mask_bit() in Xen was triggered. After adding "WARN_ON(1)"
> to that place, I got the call trace below:
> 
> (XEN) Xen call trace:
> (XEN)    [<ffff82d080281a6a>] msi.c#msi_set_mask_bit+0x1da/0x29b
> (XEN)    [<ffff82d080282e78>] guest_mask_msi_irq+0x1c/0x1e
> (XEN)    [<ffff82d08030ceb9>] vmsi.c#msixtbl_write+0x173/0x1d4
> (XEN)    [<ffff82d08030cf30>] vmsi.c#_msixtbl_write+0x16/0x18
> (XEN)    [<ffff82d0802ffac4>] hvm_process_io_intercept+0x216/0x270
> (XEN)    [<ffff82d0802ffb45>] hvm_io_intercept+0x27/0x4c
> (XEN)    [<ffff82d0802f0e86>] emulate.c#hvmemul_do_io+0x273/0x454
> (XEN)    [<ffff82d0802f10a4>] emulate.c#hvmemul_do_io_buffer+0x3d/0x70
> (XEN)    [<ffff82d0802f2343>] emulate.c#hvmemul_linear_mmio_access+0x35e/0x436
> (XEN)    [<ffff82d0802f2640>] emulate.c#linear_write+0xdd/0x13b
> (XEN)    [<ffff82d0802f3f25>] emulate.c#hvmemul_write+0xbd/0xf1
> (XEN)    [<ffff82d0802d51df>] x86_emulate+0x2249d/0x23c5c
> (XEN)    [<ffff82d0802d861f>] x86_emulate_wrapper+0x2b/0x5f
> (XEN)    [<ffff82d0802f28aa>] emulate.c#_hvm_emulate_one+0x54/0x1b2
> (XEN)    [<ffff82d0802f2a18>] hvm_emulate_one+0x10/0x12
> (XEN)    [<ffff82d080300227>] hvm_emulate_one_insn+0x42/0x14a
> (XEN)    [<ffff82d08030037e>] handle_mmio_with_translation+0x4f/0x51
> (XEN)    [<ffff82d0802f803b>] hvm_hap_nested_page_fault+0x16c/0x6d8
> (XEN)    [<ffff82d08032446a>] vmx_vmexit_handler+0x19b0/0x1f2e
> (XEN)    [<ffff82d08032995a>] vmx_asm_vmexit_handler+0xfa/0x270
> 
> It seems to me that guest is trying to mask a msi while the memory decoding
> of the device is disabled. Performing a device reset without proper method
> to avoid guest's MSI-X operation would lead to this issue.
> 
> The fix is basic - detach pci device before resetting the device.
> 
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

> ---
>  tools/libxl/libxl_pci.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
> index 87afa03..855fb71 100644
> --- a/tools/libxl/libxl_pci.c
> +++ b/tools/libxl/libxl_pci.c
> @@ -1459,17 +1459,17 @@ skip1:
>          fclose(f);
>      }
>  out:
> -    /* don't do multiple resets while some functions are still passed 
> through */
> -    if ( (pcidev->vdevfn & 0x7) == 0 ) {
> -        libxl__device_pci_reset(gc, pcidev->domain, pcidev->bus, 
> pcidev->dev, pcidev->func);
> -    }
> -
>      if (!isstubdom) {
>          rc = xc_deassign_device(ctx->xch, domid, pcidev_encode_bdf(pcidev));
>          if (rc < 0 && (hvm || errno != ENOSYS))
>              LOGED(ERROR, domainid, "xc_deassign_device failed");
>      }
>  
> +    /* don't do multiple resets while some functions are still passed 
> through */
> +    if ( (pcidev->vdevfn & 0x7) == 0 ) {
> +        libxl__device_pci_reset(gc, pcidev->domain, pcidev->bus, 
> pcidev->dev, pcidev->func);
> +    }
> +
>      stubdomid = libxl_get_stubdom_id(ctx, domid);
>      if (stubdomid != 0) {
>          libxl_device_pci pcidev_s = *pcidev;
> -- 
> 1.8.3.1
> 

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