linux-kernel - Re: [PATCH] Drivers: hv: ioctl for self targeted passthrough hvcalls

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Message-ID: <20251115062240.GA1794663@liuwe-devbox-debian-v2.local>
Date: Sat, 15 Nov 2025 06:22:40 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Anirudh Rayabharam <anirudh@...rudhrb.com>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Long Li <longli@...rosoft.com>, linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Drivers: hv: ioctl for self targeted passthrough hvcalls

On Fri, Nov 14, 2025 at 09:58:52AM +0000, Anirudh Rayabharam wrote:
> From: Anirudh Rayabharam (Microsoft) <anirudh@...rudhrb.com>
> 
> Allow MSHV_ROOT_HVCALL IOCTL on the /dev/mshv fd. This IOCTL would
> execute a passthrough hypercall targeting the root/parent partition
> i.e. HV_PARTITION_ID_SELF.
> 
> This will be useful for the VMM to query things like supported
> synthetic processor features, supported VMM capabiliites etc.
> 
> While at it, add HVCALL_GET_PARTITION_PROPERTY_EX to the allowed list of
> passthrough hypercalls.
> 
> Signed-off-by: Anirudh Rayabharam (Microsoft) <anirudh@...rudhrb.com>

This doesn't apply to hyperv-next. What's its base?

Wei

> ---
>  drivers/hv/mshv_root_main.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index 20eda00a1b5a..98f56322cd19 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -122,6 +122,7 @@ static struct miscdevice mshv_dev = {
>   */
>  static u16 mshv_passthru_hvcalls[] = {
>  	HVCALL_GET_PARTITION_PROPERTY,
> +	HVCALL_GET_PARTITION_PROPERTY_EX,
>  	HVCALL_SET_PARTITION_PROPERTY,
>  	HVCALL_INSTALL_INTERCEPT,
>  	HVCALL_GET_VP_REGISTERS,
> @@ -159,6 +160,7 @@ static int mshv_ioctl_passthru_hvcall(struct mshv_partition *partition,
>  	unsigned int pages_order;
>  	void *input_pg = NULL;
>  	void *output_pg = NULL;
> +	u64 pt_id = partition ? partition->pt_id : HV_PARTITION_ID_SELF;
>  
>  	if (copy_from_user(&args, user_args, sizeof(args)))
>  		return -EFAULT;
> @@ -180,7 +182,7 @@ static int mshv_ioctl_passthru_hvcall(struct mshv_partition *partition,
>  	is_async = mshv_hvcall_is_async(args.code);
>  	if (is_async) {
>  		/* async hypercalls can only be called from partition fd */
> -		if (!partition_locked)
> +		if (!partition || !partition_locked)
>  			return -EINVAL;
>  		ret = mshv_init_async_handler(partition);
>  		if (ret)
> @@ -208,7 +210,7 @@ static int mshv_ioctl_passthru_hvcall(struct mshv_partition *partition,
>  	 * NOTE: This only works because all the allowed hypercalls' input
>  	 * structs begin with a u64 partition_id field.
>  	 */
> -	*(u64 *)input_pg = partition->pt_id;
> +	*(u64 *)input_pg = pt_id;
>  
>  	if (args.reps)
>  		status = hv_do_rep_hypercall(args.code, args.reps, 0,
> @@ -226,7 +228,7 @@ static int mshv_ioctl_passthru_hvcall(struct mshv_partition *partition,
>  	}
>  
>  	if (hv_result(status) == HV_STATUS_INSUFFICIENT_MEMORY) {
> -		ret = hv_call_deposit_pages(NUMA_NO_NODE, partition->pt_id, 1);
> +		ret = hv_call_deposit_pages(NUMA_NO_NODE, pt_id, 1);
>  		if (!ret)
>  			ret = -EAGAIN;
>  	} else if (!hv_result_success(status)) {
> @@ -2048,6 +2050,9 @@ static long mshv_dev_ioctl(struct file *filp, unsigned int ioctl,
>  	case MSHV_CREATE_PARTITION:
>  		return mshv_ioctl_create_partition((void __user *)arg,
>  						misc->this_device);
> +	case MSHV_ROOT_HVCALL:
> +		return mshv_ioctl_passthru_hvcall(NULL, false,
> +					(void __user *)arg);
>  	}
>  
>  	return -ENOTTY;
> -- 
> 2.34.1
>