Re: [bug report] iommu/vt-d: Fix kdump kernels boot failure with scalable mode

[Dan Carpenter <dan.carpenter@oracle.com>]

On Thu, Sep 15, 2022 at 11:21:36AM +0100, Robin Murphy wrote:
> On 2022-09-15 11:05, Dan Carpenter wrote:
> > Hello Lu Baolu,
> > 
> > The patch 0c5f6c0d8201: "iommu/vt-d: Fix kdump kernels boot failure
> > with scalable mode" from Aug 23, 2022, leads to the following Smatch
> > static checker warning:
> > 
> > drivers/iommu/intel/iommu.c:224 set_context_copied() warn: set_bit() takes a bit number
> > drivers/iommu/intel/iommu.c:230 clear_context_copied() warn: clear_bit() takes a bit number
> > 
> > drivers/iommu/intel/iommu.c
> >      221 static inline void
> >      222 set_context_copied(struct intel_iommu *iommu, u8 bus, u8 devfn)
> >      223 {
> > --> 224         set_bit(((long)bus << 8) | devfn, iommu->copied_tables);
> >      225 }
> > 
> > This is trying to set a mask
> 
> No, it's simply composing a full 16-bit PCI requester ID from its two 8-bit
> components.
> 

Ah...  Okay.  That works then.

> > but it will instead corrupt a bit way out
> > in the middle of your memory.
> 
> 	iommu->copied_tables = bitmap_zalloc(BIT_ULL(16), GFP_KERNEL);
> 
> Again slightly non-obvious, but AFAICS the bitmap is sized appropriately.

Btw, just BIT(16) works until you get above 31.

regards,
dan carpenter