linux-kernel - Re: [RFC PATCH v7 07/16] arm64/mm, xpfo: temporarily map dcache regions

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Message-ID: <19e61a22-bbae-d0ae-8d41-158d4b46bf01@oracle.com>
Date:   Fri, 11 Jan 2019 11:28:19 -0700
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Tycho Andersen <tycho@...ho.ws>
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 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 ;)

--
Khalid

> 
> Tycho
> 
>>  	if (icache_is_aliasing()) {
>> +		xpfo_temp_map(kaddr, len, mapping,
>> +			      sizeof(mapping[0]) * num_pages);
>>  		__clean_dcache_area_pou(kaddr, len);
>> +		xpfo_temp_unmap(kaddr, len, mapping,
>> +			        sizeof(mapping[0]) * num_pages);
>>  		__flush_icache_all();
>>  	} else {
>>  		flush_icache_range(addr, addr + len);
>> -- 
>> 2.17.1
>>


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