Re: [PATCH v3 5/5] x86/mm: add WARN_ON_ONCE() for wrong large page mapping

[Thomas Gleixner]

On Tue, 21 Aug 2018, Bin Yang wrote:
> @@ -625,6 +625,7 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
>  
>  	psize = page_level_size(level);
>  	pmask = page_level_mask(level);
> +	addr = address & pmask;
>  
>  	/*
>  	 * Calculate the number of pages, which fit into this large
> @@ -636,6 +637,12 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
>  		cpa->numpages = numpages;
>  
>  	/*
> +	 * The old pgprot should not have any protection bit. Otherwise,
> +	 * the existing mapping is wrong already.
> +	 */
> +	WARN_ON_ONCE(needs_static_protections(old_prot, addr, psize, old_pfn));

The check itself is fine, but it just emits a warning and goes on as if
nothing happened.

We really want to think about a proper way to fix that up without overhead
for the sane case.

Thanks,

	tglx