From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3C434392C32; Fri, 24 Jul 2026 22:08:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784930909; cv=none; b=Leq1ojCe5BgKRay0Lj3pXzIkwVAkx3/FrMopMQRIpT9cyJ3pRJSDIRF7TumKzHGrdt0MyrG0x4GbVHS7bpSJDIjpxmG3tYIJVXrOAl5DqOSqpK/xkJKrqd+eIzdqb04YcbHsngTGce26qWUPJkfya20PZIVy96lIl9PAFzbs0wU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784930909; c=relaxed/simple; bh=l0U3dZ28LyDdd2d58YSyrNZlaRmSuLvYsNCrSGDqRY0=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=oWA52CDMavydFAWEIyYg2EWc9FpM9AUKWhWjrc7u8xc75SQEEyL21jCtO8XrsM5MwDfQnHIrkScQb1dRHSYwWDjsjE9UZRXb7GQJFc2a+nQYTB0S3g5AqH65UprAuujXLGp8n/zB6N16nvrxL+sxBM38tRTqPHCdL5Ua7JC4g9k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=g9HnKJXw; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="g9HnKJXw" Received: from localhost (unknown [20.191.74.188]) by linux.microsoft.com (Postfix) with ESMTPSA id 41AB220B7167; Fri, 24 Jul 2026 15:08:11 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 41AB220B7167 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1784930892; bh=PneHZPZl/NkHqkk5l4fHfLS0UqzueCtDxEOMC/7Vibs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=g9HnKJXwSrSFtOmYBvW27/+B+EVq1VupYBhB239eDqO48ckvjYjgKKMnuXOHmeOQ7 nxuezF8GF4k+Svha8uP8GFtUa64ikLRIYIzvEneuQvObtP4OouSsKKLFEcCwFvCJsg uLxl/8bNNZmq+oq55HzeaLhVAmtReB6YpyTUl/hw= Date: Fri, 24 Jul 2026 15:08:24 -0700 From: Jacob Pan To: Mukesh R Cc: hpa@zytor.com, robin.murphy@arm.com, robh@kernel.org, wei.liu@kernel.org, mhklinux@outlook.com, muislam@microsoft.com, namjain@linux.microsoft.com, magnuskulke@linux.microsoft.com, anbelski@linux.microsoft.com, linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, iommu@lists.linux.dev, linux-pci@vger.kernel.org, linux-arch@vger.kernel.org, kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com, longli@microsoft.com, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, joro@8bytes.org, will@kernel.org, lpieralisi@kernel.org, kwilczynski@kernel.org, bhelgaas@google.com, arnd@arndb.de, jacob.pan@linux.microsoft.com Subject: Re: [PATCH V4 1/9] mshv: Provide a way to get partition ID if running in a VMM process Message-ID: <20260724150824.000075a7@linux.microsoft.com> In-Reply-To: <95a1bed4-dd5a-654b-9e7a-7d5a453e3966@linux.microsoft.com> References: <20260718021949.926306-1-mrathor@linux.microsoft.com> <20260718021949.926306-2-mrathor@linux.microsoft.com> <20260723152132.000033d0@linux.microsoft.com> <95a1bed4-dd5a-654b-9e7a-7d5a453e3966@linux.microsoft.com> Organization: LSG X-Mailer: Claws Mail 3.21.0 (GTK+ 2.24.33; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-hyperv@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Hi Mukesh, On Fri, 24 Jul 2026 12:14:08 -0700 Mukesh R wrote: > On 7/23/26 15:21, Jacob Pan wrote: > > Hi Mukesh, > > Hey Jacob, pl see inline.. > > > On Fri, 17 Jul 2026 19:19:41 -0700 > > Mukesh R wrote: > > ... snip... > > >> static int > >> add_partition(struct mshv_partition *partition) > >> { > >> @@ -2073,6 +2094,7 @@ mshv_ioctl_create_partition(void __user > >> *user_arg, struct device *module_dev) goto cleanup_irq_srcu; > >> > >> partition->pt_id = pt_id; > >> + partition->pt_vmm_tgid = current->tgid; > > I wonder how robust this mechanism is to identify target partition > > via tgid. > > 1) what prevents a VMM process create more than one partition? in > > that case each partition would have the same tgid. > > Currently, none of the VMMs we support do that, and doesn't look like > there is much of a demand for it. > My point is that from kernel UAPI pov, we cannot count on user behavior nor current VMM's implementation. > > 2) IIUC, the lifetime of the partition is tied to FD, which is > > different than the lifetime of a PID. The partition FD can be > > inherited or passed to another process. The VMM tg can exit while > > the FDs can be alive. Then the tgid can be reused by another > > unrelated process, right? > > yeah, AI keeps telling me that, but not super accurate imo. > > we are using tgid and not pid. tgid is process group id, and that will > stay around as long as there is at least one process in it. if we used > pid, then that would be the case. > I understand it is tgid but don't think tgid makes difference in terms of FD lifetime. e.g. process A creates a partition, then passes the partition fd to process B over a Unix socket. Process A can then exit while process B still holds a reference to the partition file. At that point the tgid that was stored in pt_vmm_tgid can be reused by an unrelated process C, while the partition's file object remains alive. > > Would it be more robust to based this on the partition FD instead of > > tgid? > > it might be, but problem with that is we need pt-id in other cases > where that is not available: for example in > hv_iommu_domain_alloc_paging and in irq remapping paths for direct > attached devices. if we can sort that out somehow, then we can do > that. but i suspect, it would take some time to figure that out, so i > hope we can make that a future enhancement. > > For now, i've been thinking of just putting a check and returning > ENOTSUPP if a vmm tries to create another partition. > IMHO, that only solves the uniqueness issue of partition ID but not the lifetime issue. maybe EEXIST instead of ENOTSUPP? > Thanks, > -Mukesh > > >> ret = add_partition(partition); > >> if (ret) > >> diff --git a/include/asm-generic/mshyperv.h > >> b/include/asm-generic/mshyperv.h index bf601d67cecb..e8cbc4e3f7ad > >> 100644 --- a/include/asm-generic/mshyperv.h > >> +++ b/include/asm-generic/mshyperv.h > >> @@ -350,6 +350,7 @@ int hv_call_add_logical_proc(int node, u32 > >> lp_index, u32 acpi_id); int > >> hv_call_notify_all_processors_started(void); bool hv_lp_exists(u32 > >> lp_index); int hv_call_create_vp(int node, u64 partition_id, u32 > >> vp_index, u32 flags); +u64 mshv_current_partid(void); > >> > >> #else /* CONFIG_MSHV_ROOT */ > >> static inline bool hv_root_partition(void) { return false; } > >> @@ -380,6 +381,10 @@ static inline int hv_call_create_vp(int node, > >> u64 partition_id, u32 vp_index, u3 { > >> return -EOPNOTSUPP; > >> } > >> +static inline u64 mshv_current_partid(void) > >> +{ > >> + return HV_PARTITION_ID_INVALID; > >> +} > >> #endif /* CONFIG_MSHV_ROOT */ > >> > >> static inline int hv_deposit_memory(u64 partition_id, u64 > >> status)