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

From: Andy Lutomirski <luto@amacapital.net>
To: Jiri Kosina <jikos@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	Yisheng Xie <xieyisheng1@huawei.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	richard.fellner@student.tugraz.at, moritz.lipp@iaik.tugraz.at,
	daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at,
	luto@kernel.org, Linus Torvalds <torvalds@linux-foundation.org>,
	keescook@google.com, hughd@google.com, x86@kernel.org,
	Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch)
Date: Fri, 5 Jan 2018 13:29:50 -0800	[thread overview]
Message-ID: <F42FA32C-2774-4E21-8A3E-3B52F714DBFA@amacapital.net> (raw)
In-Reply-To: <nycvar.YFH.7.76.1801052213140.11852@cbobk.fhfr.pm>

> 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

> 