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The Hyper-V balloon driver installs a custom callback for handling page onlining operations performed by the memory hotplug subsystem. This custom callback is global, and overrides the default callback (generic_online_page) that Linux otherwise uses. The custom callback properly handles memory that is hot-added by the balloon driver as part of a Hyper-V hot-add region. But memory can also be hot-added directly by a device driver for a vPCI device, particularly GPUs. In such a case, the custom callback installed by the balloon driver runs, but won't find the page in its hot-add region list and doesn't online it, which could cause driver initialization failures. Fix this by having the balloon custom callback run generic_online_page() when the page isn't part of a Hyper-V hot-add region, thereby doing the default Linux behavior. This allows device driver hot-adds to work properly. Similar cases are handled the same way in the virtio-mem driver. Suggested-by: Vikram Sethi <vsethi@nvidia.com> Tested-by: Michael Frohlich <mfrohlich@microsoft.com> Reviewed-by: Michael Kelley <mhklinux@outlook.com> Signed-off-by: Jacob Pan <jacob.pan@linux.microsoft.com> Link: https://lore.kernel.org/r/20250107180918.1053933-1-jacob.pan@linux.microsoft.com Signed-off-by: Wei Liu <wei.liu@kernel.org> Message-ID: <20250107180918.1053933-1-jacob.pan@linux.microsoft.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.