Re: [PATCH v4 4/5] Drivers: hv: Ensure large page GPA mapping is PMD-aligned

[Nuno Das Neves <nunodasneves@linux.microsoft.com>]

On 10/6/2025 8:06 AM, Stanislav Kinsburskii wrote:
> With the upcoming introduction of movable pages, a region doesn't guarantee
> always having large pages mapped. Both mapping on fault and unmapping
> during PTE invalidation may not be 2M-aligned, while the hypervisor
> requires both the GFN and page count to be 2M-aligned to use the large page
> flag.
> 
> Update the logic for large page mapping in mshv_region_remap_pages() to
> require both page_offset and page_count to be PMD-aligned.
> 
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> ---
>  drivers/hv/mshv_root_main.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index b61bef6b9c132..cb462495f34b5 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -34,6 +34,8 @@
>  #include "mshv.h"
>  #include "mshv_root.h"
>  
> +#define VALUE_PMD_ALIGNED(c)			(!((c) & (PTRS_PER_PMD - 1)))
> +
>  MODULE_AUTHOR("Microsoft");
>  MODULE_LICENSE("GPL");
>  MODULE_DESCRIPTION("Microsoft Hyper-V root partition VMM interface /dev/mshv");
> @@ -1100,7 +1102,9 @@ mshv_region_remap_pages(struct mshv_mem_region *region, u32 map_flags,
>  	if (page_offset + page_count > region->nr_pages)
>  		return -EINVAL;
>  
> -	if (region->flags.large_pages)
> +	if (region->flags.large_pages &&
> +	    VALUE_PMD_ALIGNED(page_offset) &&
> +	    VALUE_PMD_ALIGNED(page_count))
>  		map_flags |= HV_MAP_GPA_LARGE_PAGE;
>  
>  	/* ask the hypervisor to map guest ram */
> 
> 

Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>