Re: [PATCH v3] mshv: Simplify GPA map/unmap hypercall helpers

[Anirudh Rayabharam <anirudh@anirudhrb.com>]

On Thu, Apr 30, 2026 at 02:52:17PM +0000, Stanislav Kinsburskii wrote:
> Clean up hv_do_map_gpa_hcall() and hv_call_unmap_gpa_pages() after the
> preceding bug-fix patches:
> 
> Move "done += completed" before the status checks so that pages mapped
> by a partially-successful batch are included in the error cleanup unmap.
> Previously these mappings were leaked on failure.
> 
> While here, improve type safety and readability:
>  - Change "int done" to "u64 done" to match the u64 page_count it is
>    compared against, avoiding signed/unsigned comparison hazards.
>  - Use u64 for loop iteration and batch size variables consistently.
>  - Add proper braces to the for-loop body in hv_do_map_gpa_hcall().
>  - Remove unnecessary "ret" variable from hv_call_unmap_gpa_pages().
>  - Simplify the error-path unmap to use "done << large_shift" directly
>    instead of mutating done in place.
> 
> v3: aligned changes by 80 colons
> v2: replaced min with min_t

This part describing the changes in various version should be placed
after the "---" line below. This way it won't appear in the final commit
log.

https://www.kernel.org/doc/html/latest/process/submitting-patches.html#commentary

Thanks,
Anirudh.

> 
> Fixes: 621191d709b14 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> ---
>  drivers/hv/mshv_root_hv_call.c |   56 +++++++++++++++-------------------------
>  1 file changed, 21 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/hv/mshv_root_hv_call.c b/drivers/hv/mshv_root_hv_call.c
> index e5992c324904a..e1f9e28d5a19b 100644
> --- a/drivers/hv/mshv_root_hv_call.c
> +++ b/drivers/hv/mshv_root_hv_call.c
> @@ -195,8 +195,8 @@ static int hv_do_map_gpa_hcall(u64 partition_id, u64 gfn, u64 page_struct_count,
>  	struct hv_input_map_gpa_pages *input_page;
>  	u64 status, *pfnlist;
>  	unsigned long irq_flags, large_shift = 0;
> -	int ret = 0, done = 0;
> -	u64 page_count = page_struct_count;
> +	u64 done = 0, page_count = page_struct_count;
> +	int ret = 0;
>  
>  	if (page_count == 0 || (pages && mmio_spa))
>  		return -EINVAL;
> @@ -213,8 +213,8 @@ static int hv_do_map_gpa_hcall(u64 partition_id, u64 gfn, u64 page_struct_count,
>  	}
>  
>  	while (done < page_count) {
> -		ulong i, completed, remain = page_count - done;
> -		int rep_count = min(remain, HV_MAP_GPA_BATCH_SIZE);
> +		u64 i, completed, remain = page_count - done;
> +		u64 rep_count = min_t(u64, remain, HV_MAP_GPA_BATCH_SIZE);
>  
>  		local_irq_save(irq_flags);
>  		input_page = *this_cpu_ptr(hyperv_pcpu_input_arg);
> @@ -224,23 +224,14 @@ static int hv_do_map_gpa_hcall(u64 partition_id, u64 gfn, u64 page_struct_count,
>  		input_page->map_flags = flags;
>  		pfnlist = input_page->source_gpa_page_list;
>  
> -		for (i = 0; i < rep_count; i++)
> -			if (flags & HV_MAP_GPA_NO_ACCESS) {
> +		for (i = 0; i < rep_count; i++) {
> +			if (flags & HV_MAP_GPA_NO_ACCESS)
>  				pfnlist[i] = 0;
> -			} else if (pages) {
> -				u64 index = (done + i) << large_shift;
> -
> -				if (index >= page_struct_count) {
> -					ret = -EINVAL;
> -					break;
> -				}
> -				pfnlist[i] = page_to_pfn(pages[index]);
> -			} else {
> +			else if (pages)
> +				pfnlist[i] = page_to_pfn(pages[(done + i) <<
> +							 large_shift]);
> +			else
>  				pfnlist[i] = mmio_spa + done + i;
> -			}
> -		if (ret) {
> -			local_irq_restore(irq_flags);
> -			break;
>  		}
>  
>  		status = hv_do_rep_hypercall(HVCALL_MAP_GPA_PAGES, rep_count, 0,
> @@ -248,29 +239,26 @@ static int hv_do_map_gpa_hcall(u64 partition_id, u64 gfn, u64 page_struct_count,
>  		local_irq_restore(irq_flags);
>  
>  		completed = hv_repcomp(status);
> +		done += completed;
>  
>  		if (hv_result_needs_memory(status)) {
>  			ret = hv_call_deposit_pages(NUMA_NO_NODE, partition_id,
>  						    HV_MAP_GPA_DEPOSIT_PAGES);
>  			if (ret)
>  				break;
> -
>  		} else if (!hv_result_success(status)) {
>  			ret = hv_result_to_errno(status);
>  			break;
>  		}
> -
> -		done += completed;
>  	}
>  
>  	if (ret && done) {
>  		u32 unmap_flags = 0;
>  
> -		if (flags & HV_MAP_GPA_LARGE_PAGE) {
> +		if (flags & HV_MAP_GPA_LARGE_PAGE)
>  			unmap_flags |= HV_UNMAP_GPA_LARGE_PAGE;
> -			done <<= large_shift;
> -		}
> -		hv_call_unmap_gpa_pages(partition_id, gfn, done, unmap_flags);
> +		hv_call_unmap_gpa_pages(partition_id, gfn,
> +					done << large_shift, unmap_flags);
>  	}
>  
>  	return ret;
> @@ -305,7 +293,7 @@ int hv_call_unmap_gpa_pages(u64 partition_id, u64 gfn, u64 page_count_4k,
>  	struct hv_input_unmap_gpa_pages *input_page;
>  	u64 status, page_count = page_count_4k;
>  	unsigned long irq_flags, large_shift = 0;
> -	int ret = 0, done = 0;
> +	u64 done = 0;
>  
>  	if (page_count == 0)
>  		return -EINVAL;
> @@ -319,8 +307,8 @@ int hv_call_unmap_gpa_pages(u64 partition_id, u64 gfn, u64 page_count_4k,
>  	}
>  
>  	while (done < page_count) {
> -		ulong completed, remain = page_count - done;
> -		int rep_count = min(remain, HV_UMAP_GPA_PAGES);
> +		u64 completed, remain = page_count - done;
> +		u64 rep_count = min_t(u64, remain, HV_UMAP_GPA_PAGES);
>  
>  		local_irq_save(irq_flags);
>  		input_page = *this_cpu_ptr(hyperv_pcpu_input_arg);
> @@ -333,15 +321,13 @@ int hv_call_unmap_gpa_pages(u64 partition_id, u64 gfn, u64 page_count_4k,
>  		local_irq_restore(irq_flags);
>  
>  		completed = hv_repcomp(status);
> -		if (!hv_result_success(status)) {
> -			ret = hv_result_to_errno(status);
> -			break;
> -		}
> -
>  		done += completed;
> +
> +		if (!hv_result_success(status))
> +			return hv_result_to_errno(status);
>  	}
>  
> -	return ret;
> +	return 0;
>  }
>  
>  int hv_call_get_gpa_access_states(u64 partition_id, u32 count, u64 gpa_base_pfn,
> 
>