On 30.06.22 13:34, Greg KH wrote:
On Mon, Jun 27, 2022 at 02:10:02PM -0400, Demi Marie Obenour wrote:commit dbe97cff7dd9f0f75c524afdd55ad46be3d15295 upstream unmap_grant_pages() currently waits for the pages to no longer be used. In https://github.com/QubesOS/qubes-issues/issues/7481, this lead to a deadlock against i915: i915 was waiting for gntdev's MMU notifier to finish, while gntdev was waiting for i915 to free its pages. I also believe this is responsible for various deadlocks I have experienced in the past. Avoid these problems by making unmap_grant_pages async. This requires making it return void, as any errors will not be available when the function returns. Fortunately, the only use of the return value is a WARN_ON(), which can be replaced by a WARN_ON when the error is detected. Additionally, a failed call will not prevent further calls from being made, but this is harmless. Because unmap_grant_pages is now async, the grant handle will be sent to INVALID_GRANT_HANDLE too late to prevent multiple unmaps of the same handle. Instead, a separate bool array is allocated for this purpose. This wastes memory, but stuffing this information in padding bytes is too fragile. Furthermore, it is necessary to grab a reference to the map before making the asynchronous call, and release the reference when the call returns. It is also necessary to guard against reentrancy in gntdev_map_put(), and to handle the case where userspace tries to map a mapping whose contents have not all been freed yet. Fixes: 745282256c75 ("xen/gntdev: safely unmap grants in case they are still in use") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx> Reviewed-by: Juergen Gross <jgross@xxxxxxxx> Link: https://lore.kernel.org/r/20220622022726.2538-1-demi@xxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Juergen Gross <jgross@xxxxxxxx> --- drivers/xen/gntdev-common.h | 7 ++ drivers/xen/gntdev.c | 142 +++++++++++++++++++++++++----------- 2 files changed, 106 insertions(+), 43 deletions(-)All now queued up, thanks.
Sorry, but I think at least the version for 5.10 is fishy, as it removes the tests for successful allocations of add->map_ops and add->unmap_ops. I need to do a thorough review of the patches (the "Reviewed-by:" tag in the patches is the one for the upstream patch). Greg, can you please wait for my explicit "okay" for the backports? Juergen
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