On 02.03.25 15:55, Ryan Roberts wrote:
Commit 49147beb0ccb ("x86/xen: allow nesting of same lazy mode") was added as a solution for a core-mm code change where arch_[enter|leave]_lazy_mmu_mode() started to be called in a nested manner; see commit bcc6cc832573 ("mm: add default definition of set_ptes()").However, now that we have fixed the API to avoid nesting, we no longer need this capability in the x86 implementation. Additionally, from code review, I don't believe the fix was ever robust in the case of preemption occurring while in the nested lazy mode. The implementation usually deals with preemption by calling arch_leave_lazy_mmu_mode() from xen_start_context_switch() for the outgoing task if we are in the lazy mmu mode. Then in xen_end_context_switch(), it restarts the lazy mode by calling arch_enter_lazy_mmu_mode() for an incoming task that was in the lazy mode when it was switched out. But arch_leave_lazy_mmu_mode() will only unwind a single level of nesting. If we are in the double nest, then it's not fully unwound and per-cpu variables are left in a bad state. So the correct solution is to remove the possibility of nesting from the higher level (which has now been done) and remove this x86-specific solution. Fixes: 49147beb0ccb ("x86/xen: allow nesting of same lazy mode")
Does this patch here deserve this tag? IIUC, it's rather a cleanup now that it was properly fixed elsewhere.
Signed-off-by: Ryan Roberts <ryan.robe...@arm.com>
Acked-by: David Hildenbrand <da...@redhat.com> -- Cheers, David / dhildenb
