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

[Liu, Yi L]

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?

> 
> >
> >> +			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?

Regards,
Yi Liu