Re: [PATCH 05/11] x86/mm: do not auto-massage page protections

Nadav Amit
2018-03-23T19:15:59Z

Dave Hansen <dave.hansen@linux.intel.com> wrote:

>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> A PTE is constructed from a physical address and a pgprotval_t.
> __PAGE_KERNEL, for instance, is a pgprot_t and must be converted
> into a pgprotval_t before it can be used to create a PTE. This is
> done implicitly within functions like set_pte() by massage_pgprot().
>
> However, this makes it very challenging to set bits (and keep them
> set) if your bit is being filtered out by massage_pgprot().
>
> This moves the bit filtering out of set_pte() and friends. For

I don’t see that set_pte() filters the bits, so I am confused by this
sentence...

> +static inline pgprotval_t check_pgprot(pgprot_t pgprot)
> +{
> + pgprotval_t massaged_val = massage_pgprot(pgprot);
> +
> + /* mmdebug.h can not be included here because of dependencies */
> +#ifdef CONFIG_DEBUG_VM
> + WARN_ONCE(pgprot_val(pgprot) != massaged_val,
> + "attempted to set unsupported pgprot: %016lx "
> + "bits: %016lx supported: %016lx\n",
> + pgprot_val(pgprot),
> + pgprot_val(pgprot) ^ massaged_val,
> + __supported_pte_mask);
> +#endif
Why not to use VM_WARN_ON_ONCE() and avoid the ifdef?