Re: [PATCH v3 3/3] PCI/MSI: Convert pci_msi_ignore_mask to per MSI domain flag
From: Roger Pau Monné
Date: Mon Mar 24 2025 - 14:00:19 EST
On Mon, Mar 24, 2025 at 03:29:46PM +0100, Daniel Gomez wrote:
>
> Hi,
>
> On Fri, Mar 21, 2025 at 09:00:09AM +0100, Jürgen Groß wrote:
> > On 20.03.25 22:07, Bjorn Helgaas wrote:
> > > On Wed, Feb 19, 2025 at 10:20:57AM +0100, Roger Pau Monne wrote:
> > > > Setting pci_msi_ignore_mask inhibits the toggling of the mask bit for both
> > > > MSI and MSI-X entries globally, regardless of the IRQ chip they are using.
> > > > Only Xen sets the pci_msi_ignore_mask when routing physical interrupts over
> > > > event channels, to prevent PCI code from attempting to toggle the maskbit,
> > > > as it's Xen that controls the bit.
> > > >
> > > > However, the pci_msi_ignore_mask being global will affect devices that use
> > > > MSI interrupts but are not routing those interrupts over event channels
> > > > (not using the Xen pIRQ chip). One example is devices behind a VMD PCI
> > > > bridge. In that scenario the VMD bridge configures MSI(-X) using the
> > > > normal IRQ chip (the pIRQ one in the Xen case), and devices behind the
> > > > bridge configure the MSI entries using indexes into the VMD bridge MSI
> > > > table. The VMD bridge then demultiplexes such interrupts and delivers to
> > > > the destination device(s). Having pci_msi_ignore_mask set in that scenario
> > > > prevents (un)masking of MSI entries for devices behind the VMD bridge.
> > > >
> > > > Move the signaling of no entry masking into the MSI domain flags, as that
> > > > allows setting it on a per-domain basis. Set it for the Xen MSI domain
> > > > that uses the pIRQ chip, while leaving it unset for the rest of the
> > > > cases.
> > > >
> > > > Remove pci_msi_ignore_mask at once, since it was only used by Xen code, and
> > > > with Xen dropping usage the variable is unneeded.
> > > >
> > > > This fixes using devices behind a VMD bridge on Xen PV hardware domains.
> > > >
> > > > Albeit Devices behind a VMD bridge are not known to Xen, that doesn't mean
> > > > Linux cannot use them. By inhibiting the usage of
> > > > VMD_FEAT_CAN_BYPASS_MSI_REMAP and the removal of the pci_msi_ignore_mask
> > > > bodge devices behind a VMD bridge do work fine when use from a Linux Xen
> > > > hardware domain. That's the whole point of the series.
> > > >
> > > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > > Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > > Acked-by: Juergen Gross <jgross@xxxxxxxx>
> > >
> > > Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > >
> > > I assume you'll merge this series via the Xen tree. Let me know if
> > > otherwise.
> >
> > I've pushed the series to the linux-next branch of the Xen tree.
> >
> >
> > Juergen
>
> This patch landed in latest next-20250324 tag causing this crash:
>
> [ 0.753426] BUG: kernel NULL pointer dereference, address: 0000000000000002
> [ 0.753921] #PF: supervisor read access in kernel mode
> [ 0.754286] #PF: error_code(0x0000) - not-present page
> [ 0.754656] PGD 0 P4D 0
> [ 0.754842] Oops: Oops: 0000 [#1]
> [ 0.755080] CPU: 0 UID: 0 PID: 1 Comm: swapper Not tainted 6.14.0-rc7-next-20250324 #1 NONE
> [ 0.755691] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [ 0.756349] RIP: 0010:msix_prepare_msi_desc+0x39/0x80
> [ 0.756390] Code: 20 c7 46 04 01 00 00 00 8b 56 4c 89 d0 0d 01 01 00 00 66 89 46 4c 8b 8f 64 02 00 00 89 4e 50 48 8b 8f 70 06 00 00 48 89 4e 58 <41> f6 40 02 40 75 2a c1 ea 02 bf 80 00 00 00 21 fa 25 7f ff ff ff
> [ 0.756390] RSP: 0000:ffff8881002a76e0 EFLAGS: 00010202
> [ 0.756390] RAX: 0000000000000101 RBX: ffff88810074d000 RCX: ffffc9000002e000
> [ 0.756390] RDX: 0000000000000000 RSI: ffff8881002a7710 RDI: ffff88810074d000
> [ 0.756390] RBP: ffff8881002a7710 R08: 0000000000000000 R09: ffff8881002a76b4
> [ 0.756390] R10: 000000701000c001 R11: ffffffff82a3dc01 R12: 0000000000000000
> [ 0.756390] R13: 0000000000000005 R14: 0000000000000000 R15: 0000000000000002
> [ 0.756390] FS: 0000000000000000(0000) GS:0000000000000000(0000) knlGS:0000000000000000
> [ 0.756390] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 0.756390] CR2: 0000000000000002 CR3: 0000000002a3d001 CR4: 00000000003706b0
> [ 0.756390] Call Trace:
> [ 0.756390] <TASK>
> [ 0.756390] ? __die_body+0x1b/0x60
> [ 0.756390] ? page_fault_oops+0x2d0/0x310
> [ 0.756390] ? exc_page_fault+0x59/0xc0
> [ 0.756390] ? asm_exc_page_fault+0x22/0x30
> [ 0.756390] ? msix_prepare_msi_desc+0x39/0x80
> [ 0.756390] ? msix_capability_init+0x172/0x2c0
> [ 0.756390] ? __pci_enable_msix_range+0x1a8/0x1d0
> [ 0.756390] ? pci_alloc_irq_vectors_affinity+0x7c/0xf0
> [ 0.756390] ? vp_find_vqs_msix+0x187/0x400
> [ 0.756390] ? vp_find_vqs+0x2f/0x250
> [ 0.756390] ? snprintf+0x3e/0x50
> [ 0.756390] ? vp_modern_find_vqs+0x13/0x60
> [ 0.756390] ? init_vq+0x184/0x1e0
> [ 0.756390] ? vp_get_status+0x20/0x20
> [ 0.756390] ? virtblk_probe+0xeb/0x8d0
> [ 0.756390] ? __kernfs_new_node+0x122/0x160
> [ 0.756390] ? vp_get_status+0x20/0x20
> [ 0.756390] ? virtio_dev_probe+0x171/0x1c0
> [ 0.756390] ? really_probe+0xc2/0x240
> [ 0.756390] ? driver_probe_device+0x1d/0x70
> [ 0.756390] ? __driver_attach+0x96/0xe0
> [ 0.756390] ? driver_attach+0x20/0x20
> [ 0.756390] ? bus_for_each_dev+0x7b/0xb0
> [ 0.756390] ? bus_add_driver+0xe6/0x200
> [ 0.756390] ? driver_register+0x5e/0xf0
> [ 0.756390] ? virtio_blk_init+0x4d/0x90
> [ 0.756390] ? add_boot_memory_block+0x90/0x90
> [ 0.756390] ? do_one_initcall+0xe2/0x250
> [ 0.756390] ? xas_store+0x4b/0x4b0
> [ 0.756390] ? number+0x13b/0x260
> [ 0.756390] ? ida_alloc_range+0x36a/0x3b0
> [ 0.756390] ? parameq+0x13/0x90
> [ 0.756390] ? parse_args+0x10f/0x2a0
> [ 0.756390] ? do_initcall_level+0x83/0xb0
> [ 0.756390] ? do_initcalls+0x43/0x70
> [ 0.756390] ? rest_init+0x80/0x80
> [ 0.756390] ? kernel_init_freeable+0x70/0xb0
> [ 0.756390] ? kernel_init+0x16/0x110
> [ 0.756390] ? ret_from_fork+0x30/0x40
> [ 0.756390] ? rest_init+0x80/0x80
> [ 0.756390] ? ret_from_fork_asm+0x11/0x20
> [ 0.756390] </TASK>
> [ 0.756390] Modules linked in:
> [ 0.756390] CR2: 0000000000000002
> [ 0.756390] ---[ end trace 0000000000000000 ]---
> [ 0.756390] RIP: 0010:msix_prepare_msi_desc+0x39/0x80
> [ 0.756390] Code: 20 c7 46 04 01 00 00 00 8b 56 4c 89 d0 0d 01 01 00 00 66 89 46 4c 8b 8f 64 02 00 00 89 4e 50 48 8b 8f 70 06 00 00 48 89 4e 58 <41> f6 40 02 40 75 2a c1 ea 02 bf 80 00 00 00 21 fa 25 7f ff ff ff
> [ 0.756390] RSP: 0000:ffff8881002a76e0 EFLAGS: 00010202
> [ 0.756390] RAX: 0000000000000101 RBX: ffff88810074d000 RCX: ffffc9000002e000
> [ 0.756390] RDX: 0000000000000000 RSI: ffff8881002a7710 RDI: ffff88810074d000
> [ 0.756390] RBP: ffff8881002a7710 R08: 0000000000000000 R09: ffff8881002a76b4
> [ 0.756390] R10: 000000701000c001 R11: ffffffff82a3dc01 R12: 0000000000000000
> [ 0.756390] R13: 0000000000000005 R14: 0000000000000000 R15: 0000000000000002
> [ 0.756390] FS: 0000000000000000(0000) GS:0000000000000000(0000) knlGS:0000000000000000
> [ 0.756390] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 0.756390] CR2: 0000000000000002 CR3: 0000000002a3d001 CR4: 00000000003706b0
> [ 0.756390] note: swapper[1] exited with irqs disabled
> [ 0.782774] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
> [ 0.783560] Kernel Offset: disabled
> [ 0.783909] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009 ]---
>
>
> msix_prepare_msi_desc+0x39/0x80:
> msix_prepare_msi_desc at drivers/pci/msi/msi.c:616
> 611 desc->nvec_used = 1;
> 612 desc->pci.msi_attrib.is_msix = 1;
> 613 desc->pci.msi_attrib.is_64 = 1;
> 614 desc->pci.msi_attrib.default_irq = dev->irq;
> 615 desc->pci.mask_base = dev->msix_base;
> >616< desc->pci.msi_attrib.can_mask = !(info->flags & MSI_FLAG_NO_MASK) &&
> 617 !desc->pci.msi_attrib.is_virtual;
> 618
> 619 if (desc->pci.msi_attrib.can_mask) {
> 620 void __iomem *addr = pci_msix_desc_addr(desc);
> 621
>
> Reverting patch 3 fixes the issue.
Thanks for the report and sorry for the breakage. Do you have a QEMU
command line I can use to try to reproduce this locally?
Will work on a patch ASAP.
Regards, Roger.