On Sat, Mar 08, 2025 at 08:50:12PM -0800, Saurabh Singh Sengar wrote:
> On Mon, Feb 10, 2025 at 09:01:14PM -0800, mhkelley58@xxxxxxxxx wrote:
> > From: Michael Kelley <mhklinux@xxxxxxxxxxx>
> >
> > The VMBus driver manages the MMIO space it owns via the hyperv_mmio
> > resource tree. Because the synthetic video framebuffer portion of the
> > MMIO space is initially setup by the Hyper-V host for each guest, the
> > VMBus driver does an early reserve of that portion of MMIO space in the
> > hyperv_mmio resource tree. It saves a pointer to that resource in
> > fb_mmio. When a VMBus driver requests MMIO space and passes "true"
> > for the "fb_overlap_ok" argument, the reserved framebuffer space is
> > used if possible. In that case it's not necessary to do another request
> > against the "shadow" hyperv_mmio resource tree because that resource
> > was already requested in the early reserve steps.
> >
> > However, the vmbus_free_mmio() function currently does no special
> > handling for the fb_mmio resource. When a framebuffer device is
> > removed, or the driver is unbound, the current code for
> > vmbus_free_mmio() releases the reserved resource, leaving fb_mmio
> > pointing to memory that has been freed. If the same or another
> > driver is subsequently bound to the device, vmbus_allocate_mmio()
> > checks against fb_mmio, and potentially gets garbage. Furthermore
> > a second unbind operation produces this "nonexistent resource" error
> > because of the unbalanced behavior between vmbus_allocate_mmio() and
> > vmbus_free_mmio():
> >
> > [ 55.499643] resource: Trying to free nonexistent
> > resource <0x00000000f0000000-0x00000000f07fffff>
> >
> > Fix this by adding logic to vmbus_free_mmio() to recognize when
> > MMIO space in the fb_mmio reserved area would be released, and don't
> > release it. This filtering ensures the fb_mmio resource always exists,
> > and makes vmbus_free_mmio() more parallel with vmbus_allocate_mmio().
> >
> > Fixes: be000f93e5d7 ("drivers:hv: Track allocations of children of hv_vmbus in private resource tree")
> > Signed-off-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> > ---
> > drivers/hv/vmbus_drv.c | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> > index 2892b8da20a5..7507b3641ebd 100644
> > --- a/drivers/hv/vmbus_drv.c
> > +++ b/drivers/hv/vmbus_drv.c
> > @@ -2262,12 +2262,25 @@ void vmbus_free_mmio(resource_size_t start, resource_size_t size)
> > struct resource *iter;
> >
> > mutex_lock(&hyperv_mmio_lock);
> > +
> > + /*
> > + * If all bytes of the MMIO range to be released are within the
> > + * special case fb_mmio shadow region, skip releasing the shadow
> > + * region since no corresponding __request_region() was done
> > + * in vmbus_allocate_mmio().
> > + */
> > + if (fb_mmio && (start >= fb_mmio->start) &&
> > + (start + size - 1 <= fb_mmio->end))
> > + goto skip_shadow_release;
> > +
> > for (iter = hyperv_mmio; iter; iter = iter->sibling) {
> > if ((iter->start >= start + size) || (iter->end <= start))
> > continue;
> >
> > __release_region(iter, start, size);
> > }
> > +
> > +skip_shadow_release:
> > release_mem_region(start, size);
> > mutex_unlock(&hyperv_mmio_lock);
> >
> > --
> > 2.25.1
> >
>
> Thanks for the fix.
> There are couple of checkpatch.pl --strict CHECK, post fixing that:
>
> Tested-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
I will wait for a new version with the checkpatch.pl issues fixed.
Wei.
