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Message-ID: <w4oqfhyocmpde74n3k4c5wqqnjjwmma2rd7panjir72or5ub6q@4st4eudtajlp>
Date: Mon, 24 Mar 2025 21:45:08 +0100
From: Daniel Gomez <da.gomez@...nel.org>
To: Roger Pau Monné <roger.pau@...rix.com>
Cc: Jürgen Groß <jgross@...e.com>,
Bjorn Helgaas <helgaas@...nel.org>, linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
linux-pci@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Bjorn Helgaas <bhelgaas@...gle.com>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 3/3] PCI/MSI: Convert pci_msi_ignore_mask to per MSI
domain flag
On Mon, Mar 24, 2025 at 08:18:01PM +0100, Roger Pau Monné wrote:
> On Mon, Mar 24, 2025 at 07:58:14PM +0100, Daniel Gomez wrote:
> > On Mon, Mar 24, 2025 at 06:51:54PM +0100, Roger Pau Monné wrote:
> > > 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@...rix.com>
> > > > > > > Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
> > > > > > > Acked-by: Juergen Gross <jgross@...e.com>
> > > > > >
> > > > > > Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> > > > > >
> > > > > > 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.
> >
> > Thanks for the quick reply.
> >
> > The issue is that info appears to be uninitialized. So, this worked for me:
>
> Indeed, irq_domain->host_data is NULL, there's no msi_domain_info. As
> this is x86, I was expecting x86 ot always use
> x86_init_dev_msi_info(), but that doesn't seem to be the case. I
> would like to better understand this.
>
> > diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
> > index dcbb4f9ac578..b76c7ec33602 100644
> > --- a/drivers/pci/msi/msi.c
> > +++ b/drivers/pci/msi/msi.c
> > @@ -609,8 +609,10 @@ void msix_prepare_msi_desc(struct pci_dev *dev, struct msi_desc *desc)
> > desc->pci.msi_attrib.is_64 = 1;
> > desc->pci.msi_attrib.default_irq = dev->irq;
> > desc->pci.mask_base = dev->msix_base;
> > - desc->pci.msi_attrib.can_mask = !(info->flags & MSI_FLAG_NO_MASK) &&
> > - !desc->pci.msi_attrib.is_virtual;
> > + desc->pci.msi_attrib.can_mask =
> > + info ? !(info->flags & MSI_FLAG_NO_MASK) &&
> > + !desc->pci.msi_attrib.is_virtual :
> > + 1;
> >
> > if (desc->pci.msi_attrib.can_mask) {
> > void __iomem *addr = pci_msix_desc_addr(desc);
> > @@ -743,7 +745,7 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
> > /* Disable INTX */
> > pci_intx_for_msi(dev, 0);
> >
> > - if (!(info->flags & MSI_FLAG_NO_MASK)) {
> > + if (info && !(info->flags & MSI_FLAG_NO_MASK)) {
>
> I think this should rather be:
>
> if (!info || !(info->flags & MSI_FLAG_NO_MASK)) {
>
> So that in case of no info the default action is to mask the entries.
>
> > /*
> > * Ensure that all table entries are masked to prevent
> > * stale entries from firing in a crash kernel.
> >
> > I also noticed d (struct irq_domain) can return NULL if CONFIG_GENERIC_MSI_IRQ
> > is not set and we are not checking that either.
> >
> > I run QEMU with vmctl [1]. This is my command:
> >
> > [1] https://github.com/SamsungDS/vmctl
> >
> > /usr/bin/qemu-system-x86_64 \
> > -nodefaults \
> > -display "none" \
> > -machine "q35,accel=kvm,kernel-irqchip=split" \
> > -cpu "host" \
> > -smp "4" \
> > -m "8G" \
> > -device "intel-iommu,intremap=on" \
> > -netdev "user,id=net0,hostfwd=tcp::2222-:22" \
> > -device "virtio-net-pci,netdev=net0" \
> > -device "virtio-rng-pci" \
> > -drive "id=boot,file=file.qcow2,format=qcow2,if=virtio,discard=unmap,media=disk,read-only=no" \
> > -device "pcie-root-port,id=pcie_root_port0,chassis=1,slot=0" \
> > -device "nvme,id=nvme0,serial=deadbeef,bus=pcie_root_port0,mdts=7" \
> > -drive "id=nvm,file=~/nvm.img,format=raw,if=none,discard=unmap,media=disk,read-only=no" \
> > -device "nvme-ns,id=nvm,drive=nvm,bus=nvme0,nsid=1,logical_block_size=4096,physical_block_size=4096" \
> > -pidfile "~/vmctl/confdir/run/nvme/pidfile" \
> > -kernel "~/src/kernel/linux/arch/x86_64/boot/bzImage" \
> > -append "root=/dev/vda1 console=ttyS0,115200 audit=0" \
> > -virtfs "local,path=~/linux,security_model=none,readonly=on,mount_tag=kernel_dir" \
> > -serial "mon:stdio" \
> > -d "guest_errors" \
> > -D "~/vmctl/confdir/log/nvme/qemu.log"
>
> Can you narrow down the command line to the minimum required to
> reproduce the issue?
/usr/bin/qemu-system-x86_64 \
-nodefaults \
-display "none" \
-machine "q35,accel=kvm" \
-cpu "host" \
-drive "id=boot,file=file.qcow2,format=qcow2,if=virtio,discard=unmap,media=disk,read-only=no" \
-kernel "~/src/kernel/linux/arch/x86_64/boot/bzImage" \
-append "root=/dev/vda1 console=ttyS0,115200 audit=0" \
-serial "mon:stdio"
>
> Can you attach the Kconfig used to build the crashing kernel?
I'm using these fragments [1]:
tinyconfig kvm_guest.config virtio-fs.config systemd.config distro.config \
storage.config localauto.config
[1] https://github.com/dkruces/linux-config-fragments/
>
> Thanks, Roger.
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