Re: [PATCH v2] x86/mm/tlb: ignore f->new_tlb_gen when zero

Dave Hansen
2022-07-19T16:15:00Z

On 7/10/22 16:28, Nadav Amit wrote:
> From: Nadav Amit <namit@vmware.com>
>
> Commit aa44284960d5 ("x86/mm/tlb: Avoid reading mm_tlb_gen when
> possible") introduced an optimization of skipping the flush if the TLB
> generation that is flushed (as provided in flush_tlb_info) was already
> flushed.
>
> However, arch_tlbbatch_flush() does not provide any generation in
> flush_tlb_info. As a result, try_to_unmap_one() would not perform any
> TLB flushes.
>
> Fix it by checking whether f->new_tlb_gen is nonzero. Zero value is
> anyhow is an invalid generation value. To avoid future confusions,
> introduce TLB_GENERATION_INVALID constant and use it properly. Add some
> assertions to check no partial flushes are done with
> TLB_GENERATION_INVALID or when f->mm is NULL, since this does not make
> any sense.
>
> In addition, add the missing unlikely().

I've applied this:

> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/mm&id=8f1d56f64f8d6b80dea2d1978d10071132a695c5

Please double-check that my rewording of the commit message looks good
to you. I also replaced the VM_BUG_ON()'s with warnings. Screwing up
TLB flushing isn't great, but it's also not worth killing the system.