RE: [PATCH v1 4/4] iommu/hyperv: Add page-selective IOTLB flush support

[Michael Kelley]

From: Michael Kelley <mhklinux@xxxxxxxxxxx> Sent: Thursday, May 14, 2026 11:14 AM
> 
> From: Yu Zhang <zhangyu1@xxxxxxxxxxxxxxxxxxx> Sent: Monday, May 11, 2026 9:24 AM
> >
> > Add page-selective IOTLB flush using HVCALL_FLUSH_DEVICE_DOMAIN_LIST.
> > This hypercall accepts a list of (page_number, page_mask_shift) entries,
> > enabling finer-grained IOTLB invalidation compared to the domain-wide
> > HVCALL_FLUSH_DEVICE_DOMAIN used by hv_iommu_flush_iotlb_all().
> >
> > hv_iommu_fill_iova_list() decomposes a contiguous IOVA range into a
> > minimal set of aligned power-of-two regions that fit in a single
> > hypercall input page. When the range exceeds the page capacity, the
> > code falls back to a full domain flush automatically.
> >
> > Signed-off-by: Yu Zhang <zhangyu1@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Easwar Hariharan <easwar.hariharan@xxxxxxxxxxxxxxxxxxx>
> > ---
> >  drivers/iommu/hyperv/iommu.c | 91 +++++++++++++++++++++++++++++++++++-
> >  include/hyperv/hvgdk_mini.h  |  1 +
> >  include/hyperv/hvhdk_mini.h  | 17 +++++++
> >  3 files changed, 108 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/hyperv/iommu.c b/drivers/iommu/hyperv/iommu.c
> > index e5fc625314b5..3bca362b7815 100644
> > --- a/drivers/iommu/hyperv/iommu.c
> > +++ b/drivers/iommu/hyperv/iommu.c
> > @@ -486,10 +486,98 @@ static void hv_iommu_flush_iotlb_all(struct iommu_domain *domain)
> >  	hv_flush_device_domain(to_hv_iommu_domain(domain));
> >  }
> >
> > +/* Max number of iova_list entries in a single hypercall input page. */
> > +#define HV_IOMMU_MAX_FLUSH_VA_COUNT \
> > +	((HV_HYP_PAGE_SIZE - sizeof(struct hv_input_flush_device_domain_list)) / \
> > +	 sizeof(union hv_iommu_flush_va))
> > +
> > +/* Returned by hv_iommu_fill_iova_list() when the range exceeds the capacity */
> > +#define HV_IOMMU_FLUSH_VA_OVERFLOW	U16_MAX
> > +
> > +static inline u16 hv_iommu_fill_iova_list(union hv_iommu_flush_va *iova_list,
> > +					  unsigned long start,
> > +					  unsigned long end)
> > +{
> > +	unsigned long start_pfn = start >> PAGE_SHIFT;
> > +	unsigned long end_pfn = PAGE_ALIGN(end) >> PAGE_SHIFT;
> 
> "end" is an inclusive end address per comment in struct iommu_iotlb_gather.
> So a page aligned value would typically have 0xFFF as the low order 12 bits,
> and PAGE_ALIGN() will do the right thing. But I don't think the value is
> *required* to be page aligned.  If the value of "end" had 0x000 as the
> low order 12 bits, the above calculation would fail to include the page
> that has the address ending in 0x000.  I think it needs to be
> PAGE_ALIGN(end + 1) in order to work correctly for this corner case.
> 

One follow-on comment:  the macros HVPFN_UP() and HVPFN_DOWN()
would likely be useful in setting start_pfn and end_pfn.

Michael