linux-kernel - Re: [PATCH v0 04/15] mshv: Provide a way to get partition id if running in a VMM process

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Message-ID: <420bf947-2dc5-4a6b-9766-0eff4d1e1618@linux.microsoft.com>
Date: Fri, 23 Jan 2026 10:23:04 -0800
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Mukesh R <mrathor@...ux.microsoft.com>, linux-kernel@...r.kernel.org,
 linux-hyperv@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev, linux-pci@...r.kernel.org, linux-arch@...r.kernel.org
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com, longli@...rosoft.com, catalin.marinas@....com,
 will@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, joro@...tes.org,
 lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org,
 robh@...nel.org, bhelgaas@...gle.com, arnd@...db.de, mhklinux@...look.com,
 romank@...ux.microsoft.com
Subject: Re: [PATCH v0 04/15] mshv: Provide a way to get partition id if
 running in a VMM process

On 1/19/2026 10:42 PM, Mukesh R wrote:
> From: Mukesh Rathor <mrathor@...ux.microsoft.com>
> 
> Many PCI passthru related hypercalls require partition id of the target
> guest. Guests are actually managed by MSHV driver and the partition id
> is only maintained there. Add a field in the partition struct in MSHV
> driver to save the tgid of the VMM process creating the partition,
> and add a function there to retrieve partition id if valid VMM tgid.
> 
> Signed-off-by: Mukesh Rathor <mrathor@...ux.microsoft.com>
> ---
>  drivers/hv/mshv_root.h         |  1 +
>  drivers/hv/mshv_root_main.c    | 35 +++++++++++++++++++++++++++-------
>  include/asm-generic/mshyperv.h |  1 +
>  3 files changed, 30 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
> index 3c1d88b36741..c3753b009fd8 100644
> --- a/drivers/hv/mshv_root.h
> +++ b/drivers/hv/mshv_root.h
> @@ -134,6 +134,7 @@ struct mshv_partition {
>  
>  	struct mshv_girq_routing_table __rcu *pt_girq_tbl;
>  	u64 isolation_type;
> +	pid_t pt_vmm_tgid;
>  	bool import_completed;
>  	bool pt_initialized;
>  };
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index 1134a82c7881..83c7bad269a0 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -1823,6 +1823,20 @@ mshv_partition_release(struct inode *inode, struct file *filp)
>  	return 0;
>  }
>  
> +/* Given a process tgid, return partition id if it is a VMM process */
> +u64 mshv_pid_to_partid(pid_t tgid)
> +{
> +	struct mshv_partition *pt;
> +	int i;
> +
> +	hash_for_each_rcu(mshv_root.pt_htable, i, pt, pt_hnode)
> +		if (pt->pt_vmm_tgid == tgid)
> +			return pt->pt_id;
> +
> +	return HV_PARTITION_ID_INVALID;
> +}
> +EXPORT_SYMBOL_GPL(mshv_pid_to_partid);
> +
>  static int
>  add_partition(struct mshv_partition *partition)
>  {
> @@ -1987,13 +2001,20 @@ mshv_ioctl_create_partition(void __user *user_arg, struct device *module_dev)
>  		goto delete_partition;
>  
>  	ret = mshv_init_async_handler(partition);
> -	if (!ret) {
> -		ret = FD_ADD(O_CLOEXEC, anon_inode_getfile("mshv_partition",
> -							   &mshv_partition_fops,
> -							   partition, O_RDWR));
> -		if (ret >= 0)
> -			return ret;
> -	}
> +	if (ret)
> +		goto rem_partition;
> +
> +	ret = FD_ADD(O_CLOEXEC, anon_inode_getfile("mshv_partition",
> +						   &mshv_partition_fops,
> +						   partition, O_RDWR));
> +	if (ret < 0)
> +		goto rem_partition;
> +
> +	partition->pt_vmm_tgid = current->tgid;
> +
> +	return ret;
> +
> +rem_partition:
>  	remove_partition(partition);
>  delete_partition:
>  	hv_call_delete_partition(partition->pt_id);
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index ecedab554c80..e46a38916e76 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -211,6 +211,7 @@ void __init ms_hyperv_late_init(void);
>  int hv_common_cpu_init(unsigned int cpu);
>  int hv_common_cpu_die(unsigned int cpu);
>  void hv_identify_partition_type(void);
> +u64 mshv_pid_to_partid(pid_t tgid);

This should go inside the #if IS_ENABLED(CONFIG_MSHV_ROOT) section.

>  
>  /**
>   * hv_cpu_number_to_vp_number() - Map CPU to VP.