Re: kernel NULL pointer dereference in quirk_clear_strap_no_soft_reset_dev2_f0 -> amd_smn_read

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Fri, Jun 05, 2026 at 12:36:29PM -0500, Mario Limonciello wrote:
> 
> 
> On 6/5/26 12:34, Marek Marczykowski-Górecki wrote:
> > On Mon, Jan 12, 2026 at 08:47:50PM -0600, Mario Limonciello wrote:
> > > 
> > > 
> > > On 1/12/2026 7:01 PM, Marek Marczykowski-Górecki wrote:
> > > > Hi,
> > > > 
> > > > I've got a report that kernel 6.17.9 crashes when running a Xen HVM domU
> > > > with AMD Raphael/Granite Ridge USB controller passed through.
> > > > It worked correctly in 6.12.59. Between those versions, I don't see any
> > > > relevant change to quirk_clear_strap_no_soft_reset_dev2_f0() function,
> > > > but the AMD node driver did got some changes, so my guess is one of them
> > > > is to blame. I know the good-bad range is huge, but there aren't that
> > > > many changes to the AMD node driver in this range.
> > > 
> > > Is this perhaps a case that only the USB controller was passed through but
> > > that the root controller wasn't?  That would lead to a case that
> > > amd_smn_init() was never called and thus amd_roots was not initialized
> > > properly.
> > > 
> > > So it would be a NULL pointer deref.  If that's correct, something like this
> > > should work to avoid it.
> > > 
> > > diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
> > > index 3d0a4768d603c..894823b444d47 100644
> > > --- a/arch/x86/kernel/amd_node.c
> > > +++ b/arch/x86/kernel/amd_node.c
> > > @@ -91,6 +91,11 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32
> > > address, u32 *value, b
> > >          if (node >= amd_num_nodes())
> > >                  return err;
> > > 
> > > +       if (!amd_roots) {
> > > +               pr_warn("AMD SMN roots not initialized.\n");
> > > +               return err;
> > > +       }
> > > +
> > >          root = amd_roots[node];
> > >          if (!root)
> > >                  return err;
> > 
> > Thanks, I finally got confirmation from affected user that this patch
> > fixes the issue. From what I understand, adbf61cc47cb ("x86/acpi/boot: Correct
> > acpi_is_processor_usable() check again") was not enough.
> > 
> > > > Original report at (with full kernel log etc): https://forum.qubes-os.org/t/yet-another-usb-keyboard-thread/38355/8
> > 
> 
> There's another patch being discussed.  Could this help?
> 
> https://lore.kernel.org/all/20260602184823.GKah8ld2QJLm28xoa9@fat_crate.local/

Especially with 2/2 patch there, yes, looks like it would help too.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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