Re: [PATCH v2 0/5] riscv: kfence: Handle the spurious fault after kfence_unprotect(), and related fixes

[Paul Walmsley]

On Tue, 3 Mar 2026, Vivian Wang wrote:

> kfence_unprotect() on RISC-V doesn't flush TLBs, because we can't send
> IPIs in some contexts where kfence objects are allocated. This leads to
> spurious faults and kfence false positives.
> 
> Avoid these spurious faults using the same "new_vmalloc" mechanism,
> which I have renamed new_valid_map_cpus to avoid confusion, since the
> kfence pool comes from the linear mapping, not vmalloc.
> 
> Commit b3431a8bb336 ("riscv: Fix IPIs usage in kfence_protect_page()")
> only seemed to consider false negatives, which are indeed tolerable.
> False positives on the other hand are not okay since they waste
> developer time (or just my time somehow?) and spam kmsg making
> diagnosing other problems difficult.
> 
> Patch 2 is the implementation to poke (what was called) new_vmalloc upon
> kfence_unprotect(). Patch 1 is some refactoring that patch 2 depends on.
> Patch 3 through 5 are some additional refactoring and minor fixes.

Thanks, queued for v7.2.


- Paul