Re: git: 36b855f18925 - main - amd64/vmm: Lock global PCI passthrough structures

On Fri, 6 Feb 2026, Mark Johnston wrote:

> The branch main has been updated by markj:
>
> URL: https://cgit.FreeBSD.org/src/commit/?id=36b855f1892575cbfe1cd5455b989bfc8ae07502
>
> commit 36b855f1892575cbfe1cd5455b989bfc8ae07502
> Author:     Mark Johnston <markj@FreeBSD.org>
> AuthorDate: 2026-02-06 15:29:22 +0000
> Commit:     Mark Johnston <markj@FreeBSD.org>
> CommitDate: 2026-02-06 15:38:51 +0000
>
>    amd64/vmm: Lock global PCI passthrough structures
>
>    There is a global list of ppt-claimed devices, accessed via several
>    vmm ioctls.  The ioctls are locked by per-VM locks, but this isn't
>    sufficient to prevent multiple VMs from trying to bind a given device.
>
>    Add a sleepable lock and use that to synchronize all access to ppt
>    devices.
>
>    Reviewed by:    corvink, jhb
>    MFC after:      2 weeks
>    Differential Revision:  https://reviews.freebsd.org/D55065
> ---
> sys/amd64/vmm/io/ppt.c | 162 +++++++++++++++++++++++++++++++++----------------
> 1 file changed, 111 insertions(+), 51 deletions(-)
>
> diff --git a/sys/amd64/vmm/io/ppt.c b/sys/amd64/vmm/io/ppt.c
> index 6feac5dcbbed..b522e18e3b24 100644
> --- a/sys/amd64/vmm/io/ppt.c
> +++ b/sys/amd64/vmm/io/ppt.c
...
> int
> @@ -529,10 +558,12 @@ ppt_unmap_mmio(struct vm *vm, int bus, int slot, int func,
> 	struct pptseg *seg;
> 	struct pptdev *ppt;
>
> +	PPT_LOCK();
> 	error = ppt_find(vm, bus, slot, func, &ppt);
> 	if (error)
> -		return (error);
> +		goto out;
>
> +	error = ENOENT;
> 	for (i = 0; i < MAX_MMIOSEGS; i++) {
> 		seg = &ppt->mmio[i];
> 		if (seg->gpa == gpa && seg->len == len) {
> @@ -541,9 +572,11 @@ ppt_unmap_mmio(struct vm *vm, int bus, int slot, int func,
> 				seg->gpa = 0;
> 				seg->len = 0;
> 			}
> -			return (error);
> +			break;
> 		}
> 	}
> +out:
> +	PPT_UNLOCK();
> 	return (ENOENT);
> }

There's a bug here.  That should be return (error).  That's been breaking
pci passthru since February.  I cannot imagine how no one noticed this in
3 months?

/bz

-- 
Bjoern A. Zeeb                                                     r15:7