Re: [PATCH v4 04/12] iommu/vt-d: Add 256-bit invalidation descriptor support

[Lu Baolu]

Hi,

On 11/8/18 11:49 AM, Liu, Yi L wrote:
> Hi,
>
> > From: Lu Baolu [mailto:baolu.lu@xxxxxxxxxxxxxxx]
> > Sent: Thursday, November 8, 2018 10:17 AM
> > Subject: Re: [PATCH v4 04/12] iommu/vt-d: Add 256-bit invalidation descriptor
> > support
> >
> > Hi Yi,
> >
> > On 11/7/18 2:07 PM, Liu, Yi L wrote:
> > > Hi Baolu,
> > >
> > > > From: Lu Baolu [mailto:baolu.lu@xxxxxxxxxxxxxxx]
> > > > Sent: Monday, November 5, 2018 1:32 PM
> > >
> > > [...]
> > >
> > > > ---
> > > >    drivers/iommu/dmar.c                | 83 +++++++++++++++++++----------
> > > >    drivers/iommu/intel-svm.c           | 76 ++++++++++++++++----------
> > > >    drivers/iommu/intel_irq_remapping.c |  6 ++-
> > > >    include/linux/intel-iommu.h         |  9 +++-
> > > >    4 files changed, 115 insertions(+), 59 deletions(-)
> > > >
> > > > diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c index
> > > > d9c748b6f9e4..ec10427b98ac 100644
> > > > --- a/drivers/iommu/dmar.c
> > > > +++ b/drivers/iommu/dmar.c
> > > > @@ -1160,6 +1160,7 @@ static int qi_check_fault(struct intel_iommu
> > > > *iommu, int
> > > > index)
> > > >    	int head, tail;
> > > >    	struct q_inval *qi = iommu->qi;
> > > >    	int wait_index = (index + 1) % QI_LENGTH;
> > > > +	int shift = qi_shift(iommu);
> > > >
> > > >    	if (qi->desc_status[wait_index] == QI_ABORT)
> > > >    		return -EAGAIN;
> > > > @@ -1173,13 +1174,15 @@ static int qi_check_fault(struct intel_iommu
> > > > *iommu, int index)
> > > >    	 */
> > > >    	if (fault & DMA_FSTS_IQE) {
> > > >    		head = readl(iommu->reg + DMAR_IQH_REG);
> > > > -		if ((head >> DMAR_IQ_SHIFT) == index) {
> > > > +		if ((head >> shift) == index) {
> > > > +			struct qi_desc *desc = qi->desc + head;
> > > > +
> > > >    			pr_err("VT-d detected invalid descriptor: "
> > > >    				"low=%llx, high=%llx\n",
> > > > -				(unsigned long long)qi->desc[index].low,
> > > > -				(unsigned long long)qi->desc[index].high);
> > > > -			memcpy(&qi->desc[index], &qi->desc[wait_index],
> > > > -					sizeof(struct qi_desc));
> > > > +				(unsigned long long)desc->qw0,
> > > > +				(unsigned long long)desc->qw1);
> > >
> > > Still missing qw2 and qw3. May make the print differ based on if smts is configed.
> >
> > qw2 and qw3 are reserved from software point of view. We don't need to print it for
> > information.
>
> But for Scalable mode, it should be valid?

No. It's reserved for software.

> > > > +			memcpy(desc, qi->desc + (wait_index << shift),
> > >
> > > Would "memcpy(desc, (unsigned long long) (qi->desc +  (wait_index <<
> > > shift)," be more safe?
> >
> > Can that be compiled? memcpy() requires a "const void *" for the second parameter.
> > By the way, why it's safer with this casting?
>
> This is just an example. My point is the possibility that "qi->desc + (wait_index << shift)"
> would be treated as "qi->desc plus (wait_index << shift)*sizeof(*qi->desc)". Is it possible
> for kernel build?

qi->desc is of type of "void *".

Best regards,
Lu Baolu