On 04/11/2025 8:19 pm, Sean Christopherson wrote:
On Tue, Nov 04, 2025, Jack Thomson wrote:
On 03/11/2025 9:08 pm, Sean Christopherson wrote:
On Tue, Oct 28, 2025, Jack Thomson wrote:
On 23/10/2025 6:16 pm, Sean Christopherson wrote:
On Mon, Oct 13, 2025, Jack Thomson wrote:
From: Jack Thomson <[email protected]>
When creating a VM using mmap with huge pages, and the memory amount does
not align with the underlying page size. The stored mmap_size value does
not account for the fact that mmap will automatically align the length
to a multiple of the underlying page size. During the teardown of the
test, munmap is used. However, munmap requires the length to be a
multiple of the underlying page size.
What happens when selftests use the wrong map_size? E.g. is munmap() silently
failing? If so, then I should probably take this particular patch through
kvm-x86/gmem, otherwise it means we'll start getting asserts due to:
3223560c93eb ("KVM: selftests: Define wrappers for common syscalls to assert
success")
If munmap() isn't failing, then that begs the question of what this patch is
actually doing :-)
Hi Sean, sorry I completely missed your reply.
Yeah currently with a misaligned map_size it causes munmap() to fail, I
noticed when tested with different backings.
Exactly which tests fail? I ask because I'm not sure we want to fix this by
having vm_mem_add() paper over test issues (I vaguely recall looking at this in
the past, but I can't find or recall the details).
The test failures happened with pre_faulting tests after adding the
option to change the backing page size [1]. If you'd prefer to
have the test handle with this I'll update there instead.
Ah, yeah, that's a test bug introduced by your patch. I can't find the thread,
but the issue of hugepage aligntment in vm_mem_add() has come up in the past,
and IIRC the conclusion was that tests need to handle the size+alignment,
because
having the library force the alignment risking papering over test bugs/flaws.
And I think there may have even been cases where it introduced failures, as some
tests deliberately wanted to do weird things?
E.g. not updating the pre-faulting test to use the "correct" size+alignment
means
the test is missing easy coverage for hugepages, since KVM won't create huge
mappings in stage-2 due to the memslot not being sized+aligned.
Got you, that makes sense I'll update this series to resolve this then.
Thanks for taking a look.
--
Thanks,
Jack
