kernel/git/stable/linux-stable.git/drivers/hv, branch linux-5.15.y

Drivers: hv: vmbus: Improve the logic of reserving fb_mmio on Gen2 VMs

2026-07-04T11:39:40+00:00

[ Upstream commit 016a25e4b0df4d77e7c258edee4aaf982e4ee809 ] If vmbus_reserve_fb() in the kdump/kexec kernel fails to properly reserve the framebuffer MMIO range (which is below 4GB) due to a Gen2 VM's screen.lfb_base being zero [1], there is an MMIO conflict between the drivers hyperv-drm and pci-hyperv: when the driver pci-hyperv's hv_allocate_config_window() calls vmbus_allocate_mmio() to get an MMIO range, typically it gets a 32-bit MMIO range that overlaps with the framebuffer MMIO range, and later hv_pci_enter_d0() fails with an error message "PCI Pass-through VSP failed D0 Entry with status" since the host thinks that PCI devices must not use MMIO space that the host has assigned to the framebuffer. This is especially an issue if pci-hyperv is built-in and hyperv-drm is built as a module. Consequently, the kdump/kexec kernel fails to detect PCI devices via pci-hyperv, and may fail to mount the root file system, which may reside in a NVMe disk. The issue described here has existed for SR-IOV VF NICs since day one of the pci-hyperv driver, and has been worked around on x64 when possible. With the recent introduction of ARM64 VMs that boot from NVMe, there is no workaround, so we need a formal fix. On Gen2 VMs, if the screen.lfb_base is 0 in the kdump/kexec kernel [1], fall back to the low MMIO base, which should be equal to the framebuffer MMIO base [2] (the statement is true according to my testing on x64 Windows Server 2016, and on x64 and ARM64 Windows Server 2025 and on Azure. I checked with the Hyper-V team and they said the statement should continue to be true for Gen2 VMs). In the first kernel, screen.lfb_base is not 0; if the user specifies a very high resolution, it's not enough to only reserve 8MB: let's always reserve half of the space below 4GB, but cap the reservation to 128MB, which is the required framebuffer size of the highest resolution 7680*4320 supported by Hyper-V. While at it, fix the comparison "end > VTPM_BASE_ADDRESS" by changing the > to >=. Here the 'end' is an inclusive end (typically, it's 0xFFFF_FFFF for the low MMIO range). Note: vmbus_reserve_fb() now also reserves an MMIO range at the beginning of the low MMIO range on CVMs, which have no framebuffers (the 'screen.lfb_base' in vmbus_reserve_fb() is 0 for CVMs), just in case the host might treat the beginning of the low MMIO range specially [3]. BTW, the OpenHCL kernel is not affected by the change, because that kernel boots with DeviceTree rather than ACPI (so vmbus_reserve_fb() won't run there), and there is no framebuffer device for that kernel. Note: normally Gen1 VMs don't have the MMIO conflict issue because the framebuffer MMIO range (which is hardcoded to base=4GB-128MB and size=64MB for Gen1 VMs by the host) is always reported via the legacy PCI graphics device's BAR, so the kdump/kexec kernel can reserve the 64MB MMIO range; however, if the VM is configured to use a very high resolution and the required framebuffer size exceeds 64MB (AFAIK, in practice, this isn't a typical configuration by users), the hyperv-drm driver may need to allocate an MMIO range above 4GB and change the framebuffer MMIO location to the allocated MMIO range -- in this case, there can still be issues [4] which can't be easily fixed: any possible affected Gen1 users would have to use a resolution whose framebuffer size is <= 64MB, or switch to Gen2 VMs. [1] https://lore.kernel.org/all/SA1PR21MB692176C1BC53BFC9EAE5CF8EBF51A@SA1PR21MB6921.namprd21.prod.outlook.com/ [2] https://lore.kernel.org/all/SA1PR21MB69218F955B62DFF62E3E88D2BF222@SA1PR21MB6921.namprd21.prod.outlook.com/ [3] https://lore.kernel.org/all/SN6PR02MB415726B17D5A6027CD1717E8D4342@SN6PR02MB4157.namprd02.prod.outlook.com/ [4] https://lore.kernel.org/all/SA1PR21MB69213486F821CA5A2C793C81BF342@SA1PR21MB6921.namprd21.prod.outlook.com/ Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs") CC: stable@vger.kernel.org Reviewed-by: Michael Kelley Tested-by: Krister Johansen Tested-by: Matthew Ruffell Signed-off-by: Dexuan Cui Signed-off-by: Wei Liu Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

hv: utils: handle and propagate errors in kvp_register

2026-07-04T11:39:40+00:00

[ Upstream commit 3fcf923302a8f5c0dc3af3d2ca2657cb5fae4297 ] Make kvp_register() return an error code instead of silently ignoring failures, and propagate the error from kvp_handle_handshake() instead of returning success. This propagates both kzalloc_obj() and hvutil_transport_send() failures to kvp_handle_handshake() and thus to kvp_on_msg(). Fixes: 245ba56a52a3 ("Staging: hv: Implement key/value pair (KVP)") Cc: stable@vger.kernel.org Signed-off-by: Thorsten Blum Reviewed-by: Long Li Signed-off-by: Wei Liu Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Add utility function for querying ring size

2025-07-10T13:57:36+00:00

[ Upstream commit e8c4bd6c6e6b7e7b416c42806981c2a81370001e ] Add a function to query for the preferred ring buffer size of VMBus device. This will allow the drivers (eg. UIO) to allocate the most optimized ring buffer size for devices. Signed-off-by: Saurabh Sengar Reviewed-by: Long Li Link: https://lore.kernel.org/r/1711788723-8593-2-git-send-email-ssengar@linux.microsoft.com Signed-off-by: Greg Kroah-Hartman Stable-dep-of: 0315fef2aff9 ("uio_hv_generic: Align ring size to system page") Signed-off-by: Sasha Levin

Drivers: hv: Rename 'alloced' to 'allocated'

2025-07-10T13:57:35+00:00

[ Upstream commit de96e8a09889b35dd8d1cb6d19ef2bb123b05be1 ] 'Alloced' is not a real word and only saves us two letters, let's use 'allocated' instead. No functional change intended. Signed-off-by: Vitaly Kuznetsov Reviewed-by: Michael Kelley Link: https://lore.kernel.org/r/20220128103412.3033736-2-vkuznets@redhat.com Signed-off-by: Wei Liu Stable-dep-of: 0315fef2aff9 ("uio_hv_generic: Align ring size to system page") Signed-off-by: Sasha Levin

Drivers: hv: vmbus: Don't release fb_mmio resource in vmbus_free_mmio()

2025-04-10T12:31:49+00:00

[ Upstream commit 73fe9073c0cc28056cb9de0c8a516dac070f1d1f ] The VMBus driver manages the MMIO space it owns via the hyperv_mmio resource tree. Because the synthetic video framebuffer portion of the MMIO space is initially setup by the Hyper-V host for each guest, the VMBus driver does an early reserve of that portion of MMIO space in the hyperv_mmio resource tree. It saves a pointer to that resource in fb_mmio. When a VMBus driver requests MMIO space and passes "true" for the "fb_overlap_ok" argument, the reserved framebuffer space is used if possible. In that case it's not necessary to do another request against the "shadow" hyperv_mmio resource tree because that resource was already requested in the early reserve steps. However, the vmbus_free_mmio() function currently does no special handling for the fb_mmio resource. When a framebuffer device is removed, or the driver is unbound, the current code for vmbus_free_mmio() releases the reserved resource, leaving fb_mmio pointing to memory that has been freed. If the same or another driver is subsequently bound to the device, vmbus_allocate_mmio() checks against fb_mmio, and potentially gets garbage. Furthermore a second unbind operation produces this "nonexistent resource" error because of the unbalanced behavior between vmbus_allocate_mmio() and vmbus_free_mmio(): [ 55.499643] resource: Trying to free nonexistent resource <0x00000000f0000000-0x00000000f07fffff> Fix this by adding logic to vmbus_free_mmio() to recognize when MMIO space in the fb_mmio reserved area would be released, and don't release it. This filtering ensures the fb_mmio resource always exists, and makes vmbus_free_mmio() more parallel with vmbus_allocate_mmio(). Fixes: be000f93e5d7 ("drivers:hv: Track allocations of children of hv_vmbus in private resource tree") Signed-off-by: Michael Kelley Tested-by: Saurabh Sengar Reviewed-by: Saurabh Sengar Link: https://lore.kernel.org/r/20250310035208.275764-1-mhklinux@outlook.com Signed-off-by: Wei Liu Message-ID: <20250310035208.275764-1-mhklinux@outlook.com> Signed-off-by: Sasha Levin

Drivers: hv: util: Avoid accessing a ringbuffer not initialized yet

2025-01-09T12:28:34+00:00

commit 07a756a49f4b4290b49ea46e089cbe6f79ff8d26 upstream. If the KVP (or VSS) daemon starts before the VMBus channel's ringbuffer is fully initialized, we can hit the panic below: hv_utils: Registering HyperV Utility Driver hv_vmbus: registering driver hv_utils ... BUG: kernel NULL pointer dereference, address: 0000000000000000 CPU: 44 UID: 0 PID: 2552 Comm: hv_kvp_daemon Tainted: G E 6.11.0-rc3+ #1 RIP: 0010:hv_pkt_iter_first+0x12/0xd0 Call Trace: ... vmbus_recvpacket hv_kvp_onchannelcallback vmbus_on_event tasklet_action_common tasklet_action handle_softirqs irq_exit_rcu sysvec_hyperv_stimer0 asm_sysvec_hyperv_stimer0 ... kvp_register_done hvt_op_read vfs_read ksys_read __x64_sys_read This can happen because the KVP/VSS channel callback can be invoked even before the channel is fully opened: 1) as soon as hv_kvp_init() -> hvutil_transport_init() creates /dev/vmbus/hv_kvp, the kvp daemon can open the device file immediately and register itself to the driver by writing a message KVP_OP_REGISTER1 to the file (which is handled by kvp_on_msg() ->kvp_handle_handshake()) and reading the file for the driver's response, which is handled by hvt_op_read(), which calls hvt->on_read(), i.e. kvp_register_done(). 2) the problem with kvp_register_done() is that it can cause the channel callback to be called even before the channel is fully opened, and when the channel callback is starting to run, util_probe()-> vmbus_open() may have not initialized the ringbuffer yet, so the callback can hit the panic of NULL pointer dereference. To reproduce the panic consistently, we can add a "ssleep(10)" for KVP in __vmbus_open(), just before the first hv_ringbuffer_init(), and then we unload and reload the driver hv_utils, and run the daemon manually within the 10 seconds. Fix the panic by reordering the steps in util_probe() so the char dev entry used by the KVP or VSS daemon is not created until after vmbus_open() has completed. This reordering prevents the race condition from happening. Reported-by: Dexuan Cui Fixes: e0fa3e5e7df6 ("Drivers: hv: utils: fix a race on userspace daemons registration") Cc: stable@vger.kernel.org Signed-off-by: Michael Kelley Acked-by: Wei Liu Link: https://lore.kernel.org/r/20241106154247.2271-3-mhklinux@outlook.com Signed-off-by: Wei Liu Message-ID: <20241106154247.2271-3-mhklinux@outlook.com> Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Fix rescind handling in uio_hv_generic

2024-09-12T09:07:51+00:00

commit 6fd28941447bf2c8ca0f26fda612a1cabc41663f upstream. Rescind offer handling relies on rescind callbacks for some of the resources cleanup, if they are registered. It does not unregister vmbus device for the primary channel closure, when callback is registered. Without it, next onoffer does not come, rescind flag remains set and device goes to unusable state. Add logic to unregister vmbus for the primary channel in rescind callback to ensure channel removal and relid release, and to ensure that next onoffer can be received and handled properly. Cc: stable@vger.kernel.org Fixes: ca3cda6fcf1e ("uio_hv_generic: add rescind support") Signed-off-by: Naman Jain Reviewed-by: Saurabh Sengar Link: https://lore.kernel.org/r/20240829071312.1595-3-namjain@linux.microsoft.com Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Fix vmbus_wait_for_unload() to scan present CPUs

2023-06-28T08:29:42+00:00

commit 320805ab61e5f1e2a5729ae266e16bec2904050c upstream. vmbus_wait_for_unload() may be called in the panic path after other CPUs are stopped. vmbus_wait_for_unload() currently loops through online CPUs looking for the UNLOAD response message. But the values of CONFIG_KEXEC_CORE and crash_kexec_post_notifiers affect the path used to stop the other CPUs, and in one of the paths the stopped CPUs are removed from cpu_online_mask. This removal happens in both x86/x64 and arm64 architectures. In such a case, vmbus_wait_for_unload() only checks the panic'ing CPU, and misses the UNLOAD response message except when the panic'ing CPU is CPU 0. vmbus_wait_for_unload() eventually times out, but only after waiting 100 seconds. Fix this by looping through *present* CPUs in vmbus_wait_for_unload(). The cpu_present_mask is not modified by stopping the other CPUs in the panic path, nor should it be. Also, in a CoCo VM the synic_message_page is not allocated in hv_synic_alloc(), but is set and cleared in hv_synic_enable_regs() and hv_synic_disable_regs() such that it is set only when the CPU is online. If not all present CPUs are online when vmbus_wait_for_unload() is called, the synic_message_page might be NULL. Add a check for this. Fixes: cd95aad55793 ("Drivers: hv: vmbus: handle various crash scenarios") Cc: stable@vger.kernel.org Reported-by: John Starks Signed-off-by: Michael Kelley Reviewed-by: Vitaly Kuznetsov Link: https://lore.kernel.org/r/1684422832-38476-1-git-send-email-mikelley@microsoft.com Signed-off-by: Wei Liu Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Call hv_synic_free() if hv_synic_alloc() fails

2023-06-28T08:29:42+00:00

commit ec97e112985c2581ee61854a4b74f080f6cdfc2c upstream. Commit 572086325ce9 ("Drivers: hv: vmbus: Cleanup synic memory free path") says "Any memory allocations that succeeded will be freed when the caller cleans up by calling hv_synic_free()", but if the get_zeroed_page() in hv_synic_alloc() fails, currently hv_synic_free() is not really called in vmbus_bus_init(), consequently there will be a memory leak, e.g. hv_context.hv_numa_map is not freed in the error path. Fix this by updating the goto labels. Cc: stable@kernel.org Signed-off-by: Dexuan Cui Fixes: 4df4cb9e99f8 ("x86/hyperv: Initialize clockevents earlier in CPU onlining") Reviewed-by: Michael Kelley Link: https://lore.kernel.org/r/20230504224155.10484-1-decui@microsoft.com Signed-off-by: Wei Liu Signed-off-by: Greg Kroah-Hartman

Drivers: vmbus: Check for channel allocation before looking up relids

2023-04-13T14:48:17+00:00

[ Upstream commit 1eb65c8687316c65140b48fad27133d583178e15 ] relid2channel() assumes vmbus channel array to be allocated when called. However, in cases such as kdump/kexec, not all relids will be reset by the host. When the second kernel boots and if the guest receives a vmbus interrupt during vmbus driver initialization before vmbus_connect() is called, before it finishes, or if it fails, the vmbus interrupt service routine is called which in turn calls relid2channel() and can cause a null pointer dereference. Print a warning and error out in relid2channel() for a channel id that's invalid in the second kernel. Fixes: 8b6a877c060e ("Drivers: hv: vmbus: Replace the per-CPU channel lists with a global array of channels") Signed-off-by: Mohammed Gamal Reviewed-by: Dexuan Cui Link: https://lore.kernel.org/r/20230217204411.212709-1-mgamal@redhat.com Signed-off-by: Wei Liu Signed-off-by: Sasha Levin