On Tue, Oct 06, 2020 at 11:10:41AM -0700, David Rientjes wrote:
Thanks Peter.
The series of commits certainly expanded from my initial set that I asked about in a thread with the subject "DMA API stable backports for AMD SEV" on May 19. Turns out that switching how DMA memory is allocated based on various characteristics of the allocation and device is trickier than originally thought :) There were a number of fixes that were needed for subtleties and cornercases that folks ran into, but were addressed and have been merged by Linus. I believe it's stable in upstream and that we've been thorough in compiling a full set of changes that are required for 5.4.
Note that without this series, all SEV-enabled guests will run into the "sleeping function called from invalid context" issue in the vmalloc layer that Peter cites when using certain drivers. For such configurations, there is no way to avoid the "BUG" messages in the guest kernel when using AMD SEV unless this series is merged into an LTS kernel that the distros will then pick up.
For my 13 patches in the 30 patch series, I fully stand by Peter's backports and rationale for merge into 5.4 LTS.
Given that this "feature" has never worked in the 5.4 or older kernels, why should this be backported there? This isn't a bugfix from what I can tell, is it? And if so, what kernel version did work properly?
And if someone really wants this new feature, why can't they just use a newer kernel release?
thanks,
greg k-h