The modernization of PCIe hotplug in Linux

Posted Oct 9, 2018 19:43 UTC (Tue) by gioele (subscriber, #61675)
In reply to: The modernization of PCIe hotplug in Linux by MarcB
Parent article: The modernization of PCIe hotplug in Linux

> I think it is not even half the battle. Even if the kernel drivers are improved, userspace will still be a big issue. "Some of the memory you mapped just physically disappeared" seems not easy to handle

Can userspace talk directly to PCIe memory?

And couldn't the userspace program just have a SIGBUS handler that notices the missing hardware, cleans up the state and goes back to normality?

The modernization of PCIe hotplug in Linux

Posted Oct 10, 2018 0:47 UTC (Wed) by excors (subscriber, #95769) [Link]

Vulkan lets you explicitly allocate device-local memory (i.e. on the GPU) then map it cache-coherently into userspace.

It has the concept of "lost" devices, which causes most API calls to return errors and the application is able to clean up and try again with a new graphics device. (Of course the application might choose to just crash instead). The spec says "The host address space corresponding to device memory mapped using vkMapMemory is still valid, and host memory accesses to these mapped regions are still valid, but the contents are undefined", which I guess means the kernel can't unmap the memory when it detects the GPU has gone away (because that would likely crash the application), but could map the whole range onto a single dummy page or something.