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

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Message-ID: <vywh5euispm7c4emz2bma3upnldj2x7rthhsedwhjguv54pakz@5dy326il2de2>
Date: Sat, 15 Nov 2025 13:09:12 +0530
From: Anirudh Rayabharam <anirudh@...rudhrb.com>
To: Wei Liu <wei.liu@...nel.org>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>, 
	Haiyang Zhang <haiyangz@...rosoft.com>, 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 Sat, Nov 15, 2025 at 06:22:40AM +0000, Wei Liu wrote:
> 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?

Hmmm... I remember doing this on hyperv-next. This the parent I see:

commit f2329fd987a0da4759c307c46fd27c4d05bb7433
Author: Naman Jain <namjain@...ux.microsoft.com>
Date:   Thu Nov 13 04:41:49 2025 +0000

    Drivers: hv: Introduce mshv_vtl driver

No worries, I can rebase it on hyperv-next and send it again.

Thanks,
Anirudh.

> 
> 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
> >