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Message-ID: <20190111195037.GH4102@cisco>
Date: Fri, 11 Jan 2019 12:50:37 -0700
From: Tycho Andersen <tycho@...ho.ws>
To: Khalid Aziz <khalid.aziz@...cle.com>
Cc: juergh@...il.com, jsteckli@...zon.de, ak@...ux.intel.com,
torvalds@...ux-foundation.org, liran.alon@...cle.com,
keescook@...gle.com, konrad.wilk@...cle.com,
Juerg Haefliger <juerg.haefliger@...onical.com>,
deepa.srinivasan@...cle.com, chris.hyser@...cle.com,
tyhicks@...onical.com, dwmw@...zon.co.uk, andrew.cooper3@...rix.com,
jcm@...hat.com, boris.ostrovsky@...cle.com,
kanth.ghatraju@...cle.com, joao.m.martins@...cle.com,
jmattson@...gle.com, pradeep.vincent@...cle.com,
john.haxby@...cle.com, tglx@...utronix.de,
kirill.shutemov@...ux.intel.com, hch@....de,
steven.sistare@...cle.com, kernel-hardening@...ts.openwall.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH v7 07/16] arm64/mm, xpfo: temporarily map dcache
regions
On Fri, Jan 11, 2019 at 11:28:19AM -0700, Khalid Aziz wrote:
> On 1/11/19 7:54 AM, Tycho Andersen wrote:
> > On Thu, Jan 10, 2019 at 02:09:39PM -0700, Khalid Aziz wrote:
> >> From: Juerg Haefliger <juerg.haefliger@...onical.com>
> >>
> >> If the page is unmapped by XPFO, a data cache flush results in a fatal
> >> page fault, so let's temporarily map the region, flush the cache, and then
> >> unmap it.
> >>
> >> v6: actually flush in the face of xpfo, and temporarily map the underlying
> >> memory so it can be flushed correctly
> >>
> >> CC: linux-arm-kernel@...ts.infradead.org
> >> Signed-off-by: Juerg Haefliger <juerg.haefliger@...onical.com>
> >> Signed-off-by: Tycho Andersen <tycho@...ker.com>
> >> Signed-off-by: Khalid Aziz <khalid.aziz@...cle.com>
> >> ---
> >> arch/arm64/mm/flush.c | 7 +++++++
> >> 1 file changed, 7 insertions(+)
> >>
> >> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> >> index 30695a868107..f12f26b60319 100644
> >> --- a/arch/arm64/mm/flush.c
> >> +++ b/arch/arm64/mm/flush.c
> >> @@ -20,6 +20,7 @@
> >> #include <linux/export.h>
> >> #include <linux/mm.h>
> >> #include <linux/pagemap.h>
> >> +#include <linux/xpfo.h>
> >>
> >> #include <asm/cacheflush.h>
> >> #include <asm/cache.h>
> >> @@ -28,9 +29,15 @@
> >> void sync_icache_aliases(void *kaddr, unsigned long len)
> >> {
> >> unsigned long addr = (unsigned long)kaddr;
> >> + unsigned long num_pages = XPFO_NUM_PAGES(addr, len);
> >> + void *mapping[num_pages];
> >
> > Does this still compile with -Wvla? It was a bad hack on my part, and
> > we should probably just drop it and come up with something else :)
>
> I will make a note of it. I hope someone with better knowledge of arm64
> than me can come up with a better solution ;)
It's not just arm64, IIRC everywhere I used xpfo_temp_map() has a VLA.
I think this is in part because some of these paths don't allow
allocation failures, so we can't do a dynamic allocation. Perhaps we
need to reserve some memory for each call site?
Tycho
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