Date: Fri, 5 Jan 2018 22:14:05 +0100 (CET)
From: Jiri Kosina <jikos@kernel.org>
To: Dave Hansen <dave.hansen@linux.intel.com>
cc: 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)
In-Reply-To: <868196c9-52ed-4270-968f-97b7a6784f61@linux.intel.com>
Message-ID: <nycvar.YFH.7.76.1801052213140.11852@cbobk.fhfr.pm>
References: <20171123003438.48A0EEDE@viggo.jf.intel.com> <20171123003447.1DB395E3@viggo.jf.intel.com> <e80ac5b1-c562-fc60-ee84-30a3a40bde60@huawei.com> <93776eb2-b6d4-679a-280c-8ba558a69c34@linux.intel.com> <bda85c5e-d2be-f4ac-e2b4-4ef01d5a01a5@huawei.com>
 <20a54a5f-f4e5-2126-fb73-6a995d13d52d@linux.intel.com> <alpine.LRH.2.00.1801051909160.27010@gjva.wvxbf.pm> <282e2a56-ded1-6eb9-5ecb-22858c424bd7@linux.intel.com> <nycvar.YFH.7.76.1801052014050.11852@cbobk.fhfr.pm>
 <868196c9-52ed-4270-968f-97b7a6784f61@linux.intel.com>
User-Agent: Alpine 2.21 (LSU 202 2017-01-01)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org

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.

Thanks,

-- 
Jiri Kosina
SUSE Labs