Re: [PATCH 1/1] iommu/vt-d: Remove unnecessary WARN_ON_ONCE()

[Lu Baolu]

Hi Joerg,

On 1/17/20 5:59 PM, Joerg Roedel wrote:
> On Thu, Jan 16, 2020 at 09:52:36AM +0800, Lu Baolu wrote:
> > Address field in device TLB invalidation descriptor is qualified
> > by the S field. If S field is zero, a single page at page address
> > specified by address [63:12] is requested to be invalidated. If S
> > field is set, the least significant bit in the address field with
> > value 0b (say bit N) indicates the invalidation address range. The
> > spec doesn't require the address [N - 1, 0] to be cleared, hence
> > remove the unnecessary WARN_ON_ONCE().
> >
> > Otherwise, the caller might set "mask = MAX_AGAW_PFN_WIDTH" in order
> > to invalidating all the cached mappings on an endpoint, and below
> > overflow error will be triggered.
> >
> > [...]
> > UBSAN: Undefined behaviour in drivers/iommu/dmar.c:1354:3
> > shift exponent 64 is too large for 64-bit type 'long long unsigned int'
> > [...]
> >
> > Reported-and-tested-by: Frank <fgndev@xxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
>
> Does this need a Fixes and/or stable tag?

This doesn't cause any errors, just an unnecessary checking of

	"0 & ((1UL << 64) - 1)"

in some cases.

> Regards,
>
> 	Joerg

Best regards,
baolu