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 1F493277035; Sat, 25 Jul 2026 01:48:58 +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=1784944139; cv=none; b=djGR2wQXUWOMfjSUrgi3VN3BkiDnlF87uWDCBZN/Nk+IGqWkAAnhm6DXwJ+5pHkFLmtkS580UzhmGAELndc+uhBj3swuUUBJSaBMpTqqfKM0ReHdWYOrRPZOowbubkFGBC3oXFH4/AIruDaSWL3RQCjECpZKYOYaAM/m464Dgzk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784944139; c=relaxed/simple; bh=cAhhGF6+vyG1G87qRlzhSjIZyR/t6sDY4jzz0+T5L8M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SKsx1ZdS9kiVChLZirlg9UyQnamUcN2m6Imk++ACkn5bhQi0EL96TjbFgKQRzLa83yLWDBqdjKSzzRaB7Wvpr+yp0n6DhBOKlL0oSnQF6q2Z8i0icjfhxwFmIwwg03YeNPn3Sh48VwTeX/K+bmgHVvFGYs/z11bSrHtt/tXpaQE= 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=AyyLpo+R; 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="AyyLpo+R" Received: from [192.168.0.88] (192-184-212-33.fiber.dynamic.sonic.net [192.184.212.33]) by linux.microsoft.com (Postfix) with ESMTPSA id 5EA3220B7166; Fri, 24 Jul 2026 18:48:42 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 5EA3220B7166 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1784944123; bh=uzkljyGsJUxANu0r8p5DHn4oDXkvGWlIE0u7dL05i/w=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=AyyLpo+RISfKhLnkyHjzEVUUkrq9AIF9+RMAvvwrZI6krpW6CRRTt/PvKmlLh9hR6 IYeXehR/T7dzKw1YHMN+FibTJqC4WdksJmG/9mRC4jy3jyEzTUcrkxn9Aszw4XnGcP zQ/LLzi+0JjhEWK/Ch8J5YuNfYQ082+p8FIcw/Q0= Message-ID: Date: Fri, 24 Jul 2026 18:48:55 -0700 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.13.1 Subject: Re: [PATCH V4 1/9] mshv: Provide a way to get partition ID if running in a VMM process Content-Language: en-US To: Jacob Pan 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 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> <20260724150824.000075a7@linux.microsoft.com> From: Mukesh R In-Reply-To: <20260724150824.000075a7@linux.microsoft.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/24/26 15:08, Jacob Pan wrote: > 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. True, but as UAPI implementors, I thought we could list its limitations. For example: an fwrite() implementation can say if you don't fflush(), fwrite() can lose data! >>> 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. Confused whether you are saying that C should still be able to manage the VM without errors, or that C could cause harm because it has access to possibly recycled pt_vmm_tgid. If latter, C cannot use pt_vmm_tgid in harmful way because: if (pt->pt_vmm_tgid == current->tgid) { ret_ptid = pt->pt_id; else return : HV_PARTITION_ID_INVALID So, because C has different tgid, it will return HV_PARTITION_ID_INVALID causing hypercalls to fail with invalid parameter. >>> 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? EEXIST: A VM already exists for this process group ENOTSUPP: more than one VM is not supported for a proc group I think either are ok, but if you prefer EEXIST, that's fine too. >> 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)