Re: [PATCH] mshv: Add dedicated ioctl for GVA to GPA translation

[Anirudh Rayabharam <anirudh@anirudhrb.com>]

On Tue, Apr 28, 2026 at 10:48:24PM +0000, Stanislav Kinsburskii wrote:
> Add an MSHV_TRANSLATE_GVA ioctl on the VP fd that wraps
> HVCALL_TRANSLATE_VIRTUAL_ADDRESS_EX with transparent fault-in handling for
> movable memory regions. The passthrough path for this hypercall is retained
> for backward compatibility.
> 
> When guest-backing pages reside in movable memory regions, the mmu_notifier
> invalidation path remaps them to NO_ACCESS in the hypervisor's second-level
> address translation tables. If the VMM issues a GVA translation (e.g.
> during MMIO emulation) while a page-table page is invalidated, the
> hypervisor returns HV_TRANSLATE_GVA_GPA_NO_READ_ACCESS. The VMM cannot
> resolve this on its own.
> 
> The new ioctl detects this transient GPA access failure, faults the page
> back in via mshv_region_handle_gfn_fault(), and retries the translation
> until it succeeds or an unrecoverable error occurs.
> 
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> ---
>  drivers/hv/mshv_root.h         |    3 ++
>  drivers/hv/mshv_root_hv_call.c |   37 +++++++++++++++++++++
>  drivers/hv/mshv_root_main.c    |   69 ++++++++++++++++++++++++++++++++++++++++
>  include/hyperv/hvgdk_mini.h    |    1 +
>  include/hyperv/hvhdk.h         |   41 ++++++++++++++++++++++++
>  include/uapi/linux/mshv.h      |   10 ++++++
>  6 files changed, 161 insertions(+)
> 
> diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
> index 1f086dcb7aa1a..2e6c4414740cc 100644
> --- a/drivers/hv/mshv_root.h
> +++ b/drivers/hv/mshv_root.h
> @@ -290,6 +290,9 @@ int hv_call_delete_vp(u64 partition_id, u32 vp_index);
>  int hv_call_assert_virtual_interrupt(u64 partition_id, u32 vector,
>  				     u64 dest_addr,
>  				     union hv_interrupt_control control);
> +int hv_call_translate_virtual_address_ex(u32 vp_index, u64 partition_id,
> +					 u64 flags, u64 gva, u64 *gfn,
> +					 struct hv_translate_gva_result_ex *result);
>  int hv_call_clear_virtual_interrupt(u64 partition_id);
>  int hv_call_get_gpa_access_states(u64 partition_id, u32 count, u64 gpa_base_pfn,
>  				  union hv_gpa_page_access_state_flags state_flags,
> diff --git a/drivers/hv/mshv_root_hv_call.c b/drivers/hv/mshv_root_hv_call.c
> index e5992c324904a..9ff4ba5373f59 100644
> --- a/drivers/hv/mshv_root_hv_call.c
> +++ b/drivers/hv/mshv_root_hv_call.c
> @@ -692,6 +692,43 @@ int hv_call_get_partition_property_ex(u64 partition_id, u64 property_code,
>  	return 0;
>  }
>  
> +int hv_call_translate_virtual_address_ex(u32 vp_index, u64 partition_id,
> +					 u64 flags, u64 gva, u64 *gfn,
> +					 struct hv_translate_gva_result_ex *result)
> +{
> +	struct hv_input_translate_virtual_address *input;
> +	struct hv_output_translate_virtual_address_ex *output;
> +	unsigned long irq_flags;
> +	u64 status;
> +
> +	local_irq_save(irq_flags);
> +
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	output = *this_cpu_ptr(hyperv_pcpu_output_arg);
> +
> +	memset(input, 0, sizeof(*input));
> +	input->partition_id = partition_id;
> +	input->vp_index = vp_index;
> +	input->control_flags = flags;
> +	input->gva_page = gva >> HV_HYP_PAGE_SHIFT;
> +
> +	status = hv_do_hypercall(HVCALL_TRANSLATE_VIRTUAL_ADDRESS_EX,
> +				 input, output);
> +
> +	if (!hv_result_success(status)) {
> +		local_irq_restore(irq_flags);
> +		pr_err("%s: %s\n", __func__, hv_result_to_string(status));
> +		return hv_result_to_errno(status);
> +	}
> +
> +	*result = output->translation_result;
> +	*gfn = output->gpa_page;
> +
> +	local_irq_restore(irq_flags);
> +
> +	return 0;
> +}
> +
>  int
>  hv_call_clear_virtual_interrupt(u64 partition_id)
>  {
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index bd1359eb58dd4..2d7b6923415a8 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -898,6 +898,72 @@ mshv_vp_ioctl_get_set_state(struct mshv_vp *vp,
>  	return 0;
>  }
>  
> +static bool mshv_gpa_fault_retryable(u32 result_code)
> +{
> +	/*
> +	 * Note: HV_TRANSLATE_GVA_GPA_UNMAPPED is intentionally not handled
> +	 * here. The guest page table cannot be unmapped under normal
> +	 * operation. It may be mapped with no access during page moves,
> +	 * but a truly unmapped state indicates a kernel driver bug.
> +	 * Retrying in this case would only mask the underlying problem of
> +	 * an unmapped guest page table.
> +	 */
> +	return result_code == HV_TRANSLATE_GVA_GPA_NO_READ_ACCESS;
> +}
> +
> +static long
> +mshv_vp_ioctl_translate_gva(struct mshv_vp *vp, void __user *user_args)
> +{
> +	struct mshv_partition *partition = vp->vp_partition;
> +	struct mshv_translate_gva args;
> +	struct hv_translate_gva_result_ex result;
> +	u64 gfn, gpa;
> +	int ret;
> +
> +	if (copy_from_user(&args, user_args, sizeof(args)))
> +		return -EFAULT;
> +
> +	do {
> +		ret = hv_call_translate_virtual_address_ex(vp->vp_index,
> +							   partition->pt_id,
> +							   args.flags, args.gva,
> +							   &gfn, &result);
> +		if (ret)
> +			return ret;
> +
> +		if (mshv_gpa_fault_retryable(result.result_code)) {
> +			struct mshv_mem_region *region;
> +			bool faulted;
> +
> +			region = mshv_partition_region_by_gfn_get(partition,
> +								  gfn);
> +			if (!region)
> +				return -EFAULT;
> +
> +			faulted = false;
> +			if (region->mreg_type == MSHV_REGION_TYPE_MEM_MOVABLE)
> +				faulted = mshv_region_handle_gfn_fault(region,
> +								       gfn);
> +			mshv_region_put(region);
> +
> +			if (!faulted)
> +				return -EFAULT;
> +
> +			cond_resched();
> +		}
> +	} while (mshv_gpa_fault_retryable(result.result_code));
> +
> +	gpa = (gfn << PAGE_SHIFT) | (args.gva & ~PAGE_MASK);
> +
> +        if (copy_to_user(args.result, &result, sizeof(*args.result)))

Indentation is a bit off here.

With that fixed:

Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>