Re: [PATCH] mm: Update mask post pxd_clear_bad()

[Dev Jain]

On 14/03/25 2:14 am, Matthew Wilcox wrote:
> On Thu, Mar 13, 2025 at 11:44:14PM +0530, Dev Jain wrote:
> > Since pxd_clear_bad() is an operation changing the state of the page tables,
> > we should call arch_sync_kernel_mappings() post this.
>
> Could you explain why?  What effect does not calling
> arch_sync_kernel_mappings() have in this case?

Apologies, I again forgot to explain the userspace effect.
I just found this by code inspection, using the logic the fixes commit 
uses: we should sync when we change the pxd.

The question I have been pondering on is, what is the use of the 
pxd_bad() macros, when do we actually hit a bad state, and why don't we 
just trigger a BUG when we hit pxd_bad()?