From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EB69F2D12ED; Fri, 7 Aug 2026 15:38:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786117087; cv=none; b=JftwZV3JoK/tcrXQiKS7VwDymcdcMU0iDhqofwEeG7vRxZ2uY3UPEG2cSVsD9ihtE+wmojjcQvh/zfjOZrXEbY7xXQBo068oitdMC/aBkABYwuU0ItZfX/zlrg3eYnfDiczRvsxEYWbTFN4dgnhySHqgURIcLf9t2fUVDsdsUug= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786117087; c=relaxed/simple; bh=TXwPnk8IQuMnGYJfOn2TQ7FsWNt62x3wUGhU5DJJG54=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LcQ0G8ACYwh56i0eEPZObAcO+UBts0phvIX68RZgUdJ548HglcwLfGGw5nuNRHK1x3Ro8PzHA2oyvRAK/v512Nl4sfk8lMElSJhbVX7qz2F4cgkfSmqR4aMHavFNd/ruatFsVnii0tNvzX/Un4pEFXGCa2pYxnVav0b3HZ/p/9A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=HAumIScL; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="HAumIScL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 546F81F000E9; Fri, 7 Aug 2026 15:38:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786117085; bh=e6gwxCeXswNB2WPVxbVyF87f311RbbAWWmg5m0h6UnQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=HAumIScLpKhxrLJP4HUiptXrQ57S3y4ps1YINtchWWRuyuumv0+DlSx6iTRrTEZP1 upOkIY9vOYQfxkUWY8DDSG6FRR/DvZU3dp1VbIAc8mGABxxfbI/zzwmk3mq48nQllx w3Ra/JPX/CP8JiEHQSfw6fleZlT1HZjTSXjA9CRw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Stanislav Kinsburskii , "Anirudh Rayabharam (Microsoft)" , Wei Liu , Sasha Levin Subject: [PATCH 7.1 194/438] mshv: Order pt_vp_array publish against irqfd assertion path Date: Fri, 7 Aug 2026 16:36:30 +0200 Message-ID: <20260807143432.163696131@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260807143428.008222056@linuxfoundation.org> References: <20260807143428.008222056@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Stanislav Kinsburskii [ Upstream commit b098dc869219c15dc49bf9cf63fb5fc1481d3373 ] mshv_partition_ioctl_create_vp() initialises a VP struct (allocations, mutex_init, init_waitqueue_head, page mappings) and then publishes the pointer into partition->pt_vp_array. Several ISR paths read this array locklessly: the intercept ISR, the two scheduler ISRs, and mshv_try_assert_irq_fast() on the irqfd fast path. Of these, only mshv_try_assert_irq_fast() can structurally race the publish. It runs from an eventfd waker without holding pt_mutex, and MSHV_IRQFD does not require the target lapic_apic_id (== vp_index) to refer to an existing VP at registration time. A user can therefore register an irqfd targeting a yet-to-be-created VP, then trigger mshv_try_assert_irq_fast() concurrently with MSHV_CREATE_VP for the same index. On weakly-ordered architectures the reader can observe a non-NULL pointer in pt_vp_array before the initialising stores to the VP struct become visible, leading to use of partially-initialised fields (e.g. vp_register_page). The other ISR readers cannot reach this race: the hypervisor will not generate intercept or scheduler messages for a VP that has never been told to run, and the user can only call MSHV_RUN_VP on the VP fd returned by MSHV_CREATE_VP, which by construction is returned after the publish. Leave those readers as plain loads. Use smp_store_release() in mshv_partition_ioctl_create_vp() to publish the pointer, and pair it with smp_load_acquire() in mshv_try_assert_irq_fast(). On x86 these compile to plain accesses under TSO; on ARM64 they emit one-instruction acquire/release barriers, acceptable on this fast path. The destroy-side path (destroy_partition() clearing pt_vp_array[i] to NULL after kfree(vp)) has a separate ordering and lifetime concern that is out of scope here. Fixes: 621191d709b14 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs") Signed-off-by: Stanislav Kinsburskii Reviewed-by: Anirudh Rayabharam (Microsoft) Signed-off-by: Wei Liu Signed-off-by: Sasha Levin --- drivers/hv/mshv_eventfd.c | 9 ++++++++- drivers/hv/mshv_root_main.c | 8 +++++++- 2 files changed, 15 insertions(+), 2 deletions(-) diff --git a/drivers/hv/mshv_eventfd.c b/drivers/hv/mshv_eventfd.c index 047e5bd432381..06aef99c8298d 100644 --- a/drivers/hv/mshv_eventfd.c +++ b/drivers/hv/mshv_eventfd.c @@ -169,7 +169,14 @@ static int mshv_try_assert_irq_fast(struct mshv_irqfd *irqfd) return -EOPNOTSUPP; #endif - vp = partition->pt_vp_array[irq->lapic_apic_id]; + /* + * Pairs with smp_store_release() in mshv_partition_ioctl_create_vp(). + * MSHV_IRQFD does not require the target lapic_apic_id to refer to an + * existing VP, so this read can race a concurrent VP creation; the + * acquire ensures that a non-NULL pointer implies the VP's + * initialising stores are visible. + */ + vp = smp_load_acquire(&partition->pt_vp_array[irq->lapic_apic_id]); if (!vp->vp_register_page) return -EOPNOTSUPP; diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c index 644f9b10cbba4..8a15448e2ace9 100644 --- a/drivers/hv/mshv_root_main.c +++ b/drivers/hv/mshv_root_main.c @@ -1157,7 +1157,13 @@ mshv_partition_ioctl_create_vp(struct mshv_partition *partition, /* already exclusive with the partition mutex for all ioctls */ partition->pt_vp_count++; - partition->pt_vp_array[args.vp_index] = vp; + /* + * Pairs with smp_load_acquire() in mshv_try_assert_irq_fast(), which + * can run concurrently from an irqfd waker without holding pt_mutex. + * The release ensures the VP's initialising stores are visible to any + * reader that observes a non-NULL pointer in pt_vp_array. + */ + smp_store_release(&partition->pt_vp_array[args.vp_index], vp); goto out; -- 2.53.0