Re: [patch V3 08/11] x86/mm/cpa: Add sanity check for existing mappings

[Peter Zijlstra]

On Mon, Sep 17, 2018 at 04:29:14PM +0200, Thomas Gleixner wrote:
> +static void split_set_pte(struct cpa_data *cpa, pte_t *pte, unsigned long pfn,
> +			  pgprot_t ref_prot, unsigned long address,
> +			  unsigned long size)
> +{
> +	unsigned int npg = PFN_DOWN(size);
> +	pgprot_t prot;
> +
> +	/*
> +	 * If try_preserve_large_page() discovered an inconsistent mapping,

You just renamed that thing.. :-)

> +	 * remove the invalid protection in the split mapping.
> +	 */
> +	if (!cpa->force_static_prot)
> +		goto set;
> +
> +	prot = static_protections(ref_prot, address, pfn, npg, CPA_PROTECT);
> +
> +	if (pgprot_val(prot) == pgprot_val(ref_prot))
> +		goto set;
> +
> +	/*
> +	 * If this is splitting a PMD, fix it up. PUD splits cannot be
> +	 * fixed trivially as that would require to rescan the newly
> +	 * installed PMD mappings after returning from split_large_page()
> +	 * so an eventual further split can allocate the necessary PTE
> +	 * pages. Warn for now and revisit it in case this actually
> +	 * happens.
> +	 */
> +	if (size == PAGE_SIZE)
> +		ref_prot = prot;
> +	else
> +		pr_warn_once("CPA: Cannot fixup static protections for PUD split\n");
> +set:
> +	set_pte(pte, pfn_pte(pfn, ref_prot));
> +}