Re: [PATCH v2 2/4] KVM: selftests: Fix unaligned mmap allocations

[Sean Christopherson <seanjc@google.com>]

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 <jackabt@amazon.com>
> > > 
> > > 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).