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Message-ID: <20190214155435.GA15694@cisco>
Date: Thu, 14 Feb 2019 08:54:35 -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, akpm@...ux-foundation.org, mhocko@...e.com,
catalin.marinas@....com, will.deacon@....com, jmorris@...ei.org,
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, oao.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, labbott@...hat.com, luto@...nel.org,
dave.hansen@...el.com, peterz@...radead.org,
kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v8 07/14] arm64/mm, xpfo: temporarily map dcache
regions
Hi,
On Wed, Feb 13, 2019 at 05:01:30PM -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>
> ---
> 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..fad09aafd9d5 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];
What version does this build on? Presumably -Wvla will cause an error
here, but,
> if (icache_is_aliasing()) {
> + xpfo_temp_map(kaddr, len, mapping,
> + sizeof(mapping[0]) * num_pages);
> __clean_dcache_area_pou(kaddr, len);
Here, we map the pages to some random address via xpfo_temp_map(),
then pass the *original* address (which may not have been mapped) to
__clean_dcache_area_pou(). So I think this whole approach is wrong.
If we want to do it this way, it may be that we need some
xpfo_map_contiguous() type thing, but since we're just going to flush
it anyway, that seems a little crazy. Maybe someone who knows more
about arm64 knows a better way?
Tycho
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