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

Dave Hansen
2018-03-23T19:26:30Z

On 03/23/2018 12:15 PM, Nadav Amit wrote:
>> 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...

This was a typo/thinko. It should be pfn_pte().

>> +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?

I wanted a message. VM_WARN_ON_ONCE() doesn't let you give a message.