Patchwork [RFC,v7,07/16] arm64/mm, xpfo: temporarily map dcache regions

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Submitter Khalid Aziz
Date Jan. 10, 2019, 9:09 p.m.
Message ID <eba179acbfdea5a646c5548cb82138c1c3b74aa2.1547153058.git.khalid.aziz@oracle.com>
Download mbox | patch
Permalink /patch/697337/
State New
Headers show

Comments

Khalid Aziz - Jan. 10, 2019, 9:09 p.m.
From: Juerg Haefliger <juerg.haefliger@canonical.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@lists.infradead.org
Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
Signed-off-by: Tycho Andersen <tycho@docker.com>
Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
---
 arch/arm64/mm/flush.c | 7 +++++++
 1 file changed, 7 insertions(+)
Tycho Andersen - Jan. 11, 2019, 2:54 p.m.
On Thu, Jan 10, 2019 at 02:09:39PM -0700, Khalid Aziz wrote:
> From: Juerg Haefliger <juerg.haefliger@canonical.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@lists.infradead.org
> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
> Signed-off-by: Tycho Andersen <tycho@docker.com>
> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.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 :)

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
>
Khalid Aziz - Jan. 11, 2019, 6:28 p.m.
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@canonical.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@lists.infradead.org
>> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
>> Signed-off-by: Tycho Andersen <tycho@docker.com>
>> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.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
>>
Tycho Andersen - Jan. 11, 2019, 7:50 p.m.
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@canonical.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@lists.infradead.org
> >> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
> >> Signed-off-by: Tycho Andersen <tycho@docker.com>
> >> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.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

Patch

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];
 
 	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);