Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch)

Andy Lutomirski
2018-01-05T21:29:54Z

> On Jan 5, 2018, at 1:14 PM, Jiri Kosina <jikos@kernel.org> wrote:
>
> On Fri, 5 Jan 2018, Dave Hansen wrote:
>
>>>>> --- a/arch/x86/platform/efi/efi_64.c
>>>>> +++ b/arch/x86/platform/efi/efi_64.c
>>>>> @@ -95,6 +95,12 @@ pgd_t * __init efi_call_phys_prolog(void
>>>>> save_pgd[pgd] = *pgd_offset_k(pgd * PGDIR_SIZE);
>>>>> vaddress = (unsigned long)__va(pgd * PGDIR_SIZE);
>>>>> set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress));
>>>>> + /*
>>>>> + * pgprot API doesn't clear it for PGD
>>>>> + *
>>>>> + * Will be brought back automatically in _epilog()
>>>>> + */
>>>>> + pgd_offset_k(pgd * PGDIR_SIZE)->pgd &= ~_PAGE_NX;
>>>>> }
>>>>> __flush_tlb_all();
>>>>
>>>> Wait a sec... Where does the _PAGE_USER come from? Shouldn't we see
>>>> the &init_mm in there and *not* set _PAGE_USER?
>>>
>>> That's because pgd_populate() uses _PAGE_TABLE and not _KERNPG_TABLE for
>>> reasons that are behind me.
>>>
>>> I did put this on my TODO list, but for later.
>>>
>>> (and yes, I tried clearing _PAGE_USER from init_mm's PGD, and no obvious
>>> breakages appeared, but I wanted to give it more thought later).
>>
>> Feel free to add my Ack on this.
>
> Thanks. I'll extract the patch out of this thread and submit it
> separately, so that it doesn't get lost buried here.
>
>> I'd personally much rather muck with random relatively unused bits of
>> the efi code than touch the core PGD code.
>
> Exactly. Especially at this point.
>
>> We need to go look at it again in the 4.16 timeframe, probably.
>
> Agreed. On my TODO list already.

Can we just delete the old memmap code instead?

--Andy

>