On Mon, Apr 13, 2026 at 09:08:31PM +0000, Michael Kelley wrote:
> From: Stanislav Kinsburskii <[email protected]> Sent: Monday,
> March 30, 2026 1:04 PM
> >
> > Consolidate memory region processing to handle both valid and invalid PFNs
> > uniformly. This eliminates code duplication across remap, unmap, share, and
> > unshare operations by using a common range processing interface.
> >
> > Holes are now remapped with no-access permissions to enable
> > hypervisor dirty page tracking for precopy live migration.
> >
> > This refactoring is a precursor to an upcoming change that will map
> > present pages in movable regions upon region creation, requiring
> > consistent handling of both mapped and unmapped ranges.
> >
> > Signed-off-by: Stanislav Kinsburskii <[email protected]>
> > ---
> > drivers/hv/mshv_regions.c | 108
> > ++++++++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 95 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/hv/mshv_regions.c b/drivers/hv/mshv_regions.c
> > index b1a707d16c07..ed9c55841140 100644
> > --- a/drivers/hv/mshv_regions.c
> > +++ b/drivers/hv/mshv_regions.c
> > @@ -119,6 +119,57 @@ static long mshv_region_process_pfns(struct
> > mshv_mem_region *region,
> > return count;
> > }
> >
> > +/**
> > + * mshv_region_process_hole - Handle a hole (invalid PFNs) in a memory
> > + * region
> > + * @region : Memory region containing the hole
> > + * @flags : Flags to pass to the handler function
> > + * @pfn_offset: Starting PFN offset within the region
> > + * @pfn_count : Number of PFNs in the hole
> > + * @handler : Callback function to invoke for the hole
> > + *
> > + * Invokes the handler function for a contiguous hole with the specified
> > + * parameters.
> > + *
> > + * Return: Number of PFNs handled, or negative error code.
> > + */
> > +static long mshv_region_process_hole(struct mshv_mem_region *region,
> > + u32 flags,
> > + u64 pfn_offset, u64 pfn_count,
> > + int (*handler)(struct mshv_mem_region
> > *region,
> > + u32 flags,
> > + u64 pfn_offset,
> > + u64 pfn_count,
> > + bool huge_page))
> > +{
> > + long ret;
> > +
> > + ret = handler(region, flags, pfn_offset, pfn_count, 0);
> > + if (ret)
> > + return ret;
> > +
> > + return pfn_count;
> > +}
> > +
> > +static long mshv_region_process_chunk(struct mshv_mem_region *region,
> > + u32 flags,
> > + u64 pfn_offset, u64 pfn_count,
> > + int (*handler)(struct mshv_mem_region
> > *region,
> > + u32 flags,
> > + u64 pfn_offset,
> > + u64 pfn_count,
> > + bool huge_page))
> > +{
> > + if (pfn_valid(region->mreg_pfns[pfn_offset]))
> > + return mshv_region_process_pfns(region, flags,
> > + pfn_offset, pfn_count,
> > + handler);
> > + else
> > + return mshv_region_process_hole(region, flags,
> > + pfn_offset, pfn_count,
> > + handler);
> > +}
> > +
> > /**
> > * mshv_region_process_range - Processes a range of PFNs in a region.
> > * @region : Pointer to the memory region structure.
> > @@ -146,33 +197,47 @@ static int mshv_region_process_range(struct
> > mshv_mem_region *region,
> > u64 pfn_count,
> > bool huge_page))
> > {
> > - u64 pfn_end;
> > + u64 start, end;
> > long ret;
> >
> > - if (check_add_overflow(pfn_offset, pfn_count, &pfn_end))
> > + if (!pfn_count)
> > + return 0;
> > +
> > + if (check_add_overflow(pfn_offset, pfn_count, &end))
> > return -EOVERFLOW;
> >
> > - if (pfn_end > region->nr_pfns)
> > + if (end > region->nr_pfns)
> > return -EINVAL;
> >
> > - while (pfn_count) {
> > - /* Skip non-present pages */
> > - if (!pfn_valid(region->mreg_pfns[pfn_offset])) {
> > - pfn_offset++;
> > - pfn_count--;
> > + start = pfn_offset;
> > + end = pfn_offset + 1;
> > +
> > + while (end < pfn_offset + pfn_count) {
> > + /*
> > + * Accumulate contiguous pfns with the same validity
> > + * (valid or not).
> > + */
> > + if (pfn_valid(region->mreg_pfns[start]) ==
> > + pfn_valid(region->mreg_pfns[end])) {
> > + end++;
> > continue;
> > }
> >
> > - ret = mshv_region_process_pfns(region, flags,
> > - pfn_offset, pfn_count,
> > - handler);
> > + ret = mshv_region_process_chunk(region, flags,
> > + start, end - start,
> > + handler);
> > if (ret < 0)
> > return ret;
> >
> > - pfn_offset += ret;
> > - pfn_count -= ret;
> > + start += ret;
> > }
> >
> > + ret = mshv_region_process_chunk(region, flags,
> > + start, end - start,
> > + handler);
> > + if (ret < 0)
> > + return ret;
> > +
> > return 0;
> > }
> >
> > @@ -208,6 +273,9 @@ static int mshv_region_chunk_share(struct
> > mshv_mem_region *region,
> > u64 pfn_offset, u64 pfn_count,
> > bool huge_page)
> > {
> > + if (!pfn_valid(region->mreg_pfns[pfn_offset]))
> > + return -EINVAL;
> > +
> > if (huge_page)
> > flags |= HV_MODIFY_SPA_PAGE_HOST_ACCESS_LARGE_PAGE;
> >
> > @@ -233,6 +301,9 @@ static int mshv_region_chunk_unshare(struct
> > mshv_mem_region *region,
> > u64 pfn_offset, u64 pfn_count,
> > bool huge_page)
> > {
> > + if (!pfn_valid(region->mreg_pfns[pfn_offset]))
> > + return -EINVAL;
> > +
> > if (huge_page)
> > flags |= HV_MODIFY_SPA_PAGE_HOST_ACCESS_LARGE_PAGE;
> >
> > @@ -256,6 +327,14 @@ static int mshv_region_chunk_remap(struct
> > mshv_mem_region *region,
> > u64 pfn_offset, u64 pfn_count,
> > bool huge_page)
> > {
> > + /*
> > + * Remap missing pages with no access to let the
> > + * hypervisor track dirty pages, enabling precopy live
> > + * migration.
> > + */
> > + if (!pfn_valid(region->mreg_pfns[pfn_offset]))
> > + flags = HV_MAP_GPA_NO_ACCESS;
>
> Is it OK to wipe out any other flags that might be set? Certainly, any
> previous
> flags in PERMISSIONS_MASK should be removed, but what about ADJUSTABLE
> and NOT_CACHED?
>
Yes, this is the right approach. The HV_MAP_GPA_NO_ACCESS flag will
immediately cause a hypervisor fault on any access to the page. So
caching and adjustability no longer matter.
Thanks,
Stanislav
> > +
> > if (huge_page)
> > flags |= HV_MAP_GPA_LARGE_PAGE;
> >
> > @@ -357,6 +436,9 @@ static int mshv_region_chunk_unmap(struct
> > mshv_mem_region *region,
> > u64 pfn_offset, u64 pfn_count,
> > bool huge_page)
> > {
> > + if (!pfn_valid(region->mreg_pfns[pfn_offset]))
> > + return 0;
> > +
> > if (huge_page)
> > flags |= HV_UNMAP_GPA_LARGE_PAGE;
> >
> >
> >
>
