Re: [PATCH 4/7] mshv: Optimize memory region mapping operations

[Stanislav Kinsburskii]

On Mon, Apr 06, 2026 at 04:57:12PM +0000, Anirudh Rayabharam wrote:
> On Wed, Apr 01, 2026 at 10:12:46PM +0000, Stanislav Kinsburskii wrote:
> > Two specific operations don't require PFN iteration: region unmapping
> > and region remapping with no access. For unmapping, all frames in MSHV
> > memory regions are guaranteed to be mapped with page access, so we can
> > unmap them all without checking individual PFNs. For remapping with no
> > access, all frames are already mapped with page access, allowing us to
> > unmap them all in one pass.
> > 
> > Since neither operation needs PFN validation, iterating over PFNs is
> > redundant. Batch operations into large page-aligned chunks followed by
> > remaining pages. This eliminates PFN traversal for these operations,
> > requires no additional hypercalls compared to the PFN-checking approach,
> > and provides the simplest possible sequential execution path.
> > 
> > The optimization utilizes HV_MAP_GPA_LARGE_PAGE and
> > HV_UNMAP_GPA_LARGE_PAGE flags for aligned portions, processing only the
> > remainder with base page granularity. This removes mshv_region_chunk_unmap()
> > and mshv_region_process_range() helper functions, reducing code complexity.
> > 
> > Signed-off-by: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx>
> > ---
> >  drivers/hv/mshv_regions.c |   65 ++++++++++++++++++++++++++++++++-------------
> >  1 file changed, 46 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/hv/mshv_regions.c b/drivers/hv/mshv_regions.c
> > index 2c4215381e0b..a92381219758 100644
> > --- a/drivers/hv/mshv_regions.c
> > +++ b/drivers/hv/mshv_regions.c
> > @@ -449,27 +449,27 @@ static int mshv_region_pin(struct mshv_region *region)
> >  	return ret < 0 ? ret : -ENOMEM;
> >  }
> >  
> > -static int mshv_region_chunk_unmap(struct mshv_region *region,
> > -				   u32 flags,
> > -				   u64 pfn_offset, u64 pfn_count,
> > -				   bool huge_page)
> > +static int mshv_region_unmap(struct mshv_region *region)
> >  {
> > -	if (!pfn_valid(region->mreg_pfns[pfn_offset]))
> > -		return 0;
> > +	u64 aligned_pages, remaining_pages;
> > +	int ret = 0;
> >  
> > -	if (huge_page)
> > -		flags |= HV_UNMAP_GPA_LARGE_PAGE;
> > +	aligned_pages = ALIGN_DOWN(region->nr_pfns, PTRS_PER_PMD);
> 
> Why is it sufficient to check just the number of pages to determine
> whether we need to use the HV_UNMAP_GPA_LARGE_PAGE? Don't we need to
> check the alignment of the start address as well?
> 

Yeah, I think it's not sufficient.
I'll address this gap.

Thanks,
Stanislav

> Thanks,
> Anirudh.