Re: [PATCH v2] mshv: Simplify GPA map/unmap hypercall helpers

[Mukesh R <mrathor@linux.microsoft.com>]

On 4/29/26 09:48, 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.
> 

what changed in V2?

> 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 |   55 +++++++++++++++-------------------------
>   1 file changed, 20 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/hv/mshv_root_hv_call.c b/drivers/hv/mshv_root_hv_call.c
> index e5992c324904a..1f19a4ca824f0 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 +224,13 @@ 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]);

Entire file is 80 cols, please don't cause this one overflow.

Thanks,
-Mukesh


> +			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 +238,26 @@ 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 +292,7 @@ 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 +306,8 @@ 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 +320,13 @@ 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,
> 
>