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[PATCH] x86/mm: only allow memmap=XX!YY over existing RAM

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  [PATCH] x86/mm: only allow memmap=XX!YY over existing RAM Yigal Korman <yigal@plexistor.com> - 2016-06-20 09:40 +0200
    Re: [PATCH] x86/mm: only allow memmap=XX!YY over existing RAM Dan Williams <dan.j.williams@intel.com> - 2016-06-20 17:50 +0200
    Re: [PATCH] x86/mm: only allow memmap=XX!YY over existing RAM Johannes Thumshirn <jthumshirn@suse.de> - 2016-06-21 15:40 +0200
    Re: [PATCH] x86/mm: only allow memmap=XX!YY over existing RAM Boaz Harrosh <boaz@plexistor.com> - 2016-06-23 14:00 +0200

#1426285 — [PATCH] x86/mm: only allow memmap=XX!YY over existing RAM

Before this patch, passing a range that is beyond the physical memory
range will succeed, the user will see a /dev/pmem0 and will be able to
access it. Reads will always return 0 and writes will be silently
ignored.

I've gotten more than one bug report about mkfs.{xfs,ext4} or nvml
failing that were eventually tracked down to be wrong values passed to
memmap.

This patch prevents the above issue by instead of adding a new memory
range, only update a RAM memory range with the PRAM type. This way,
passing the wrong memmap will either not give you a pmem at all or give
you a smaller one that actually has RAM behind it.

And if someone still needs to fake a pmem that doesn't have RAM behind
it, they can simply do memmap=XX@YY,XX!YY.

Signed-off-by: Yigal Korman <yigal@plexistor.com>
---
 arch/x86/kernel/e820.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 621b501..4bd4207 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -878,7 +878,7 @@ static int __init parse_memmap_one(char *p)
 		e820_add_region(start_at, mem_size, E820_RESERVED);
 	} else if (*p == '!') {
 		start_at = memparse(p+1, &p);
-		e820_add_region(start_at, mem_size, E820_PRAM);
+		e820_update_range(start_at, mem_size, E820_RAM, E820_PRAM);
 	} else
 		e820_remove_range(mem_size, ULLONG_MAX - mem_size, E820_RAM, 1);
 
-- 
1.9.3

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#1426723

On Mon, Jun 20, 2016 at 12:33 AM, Yigal Korman <yigal@plexistor.com> wrote:
> Before this patch, passing a range that is beyond the physical memory
> range will succeed, the user will see a /dev/pmem0 and will be able to
> access it. Reads will always return 0 and writes will be silently
> ignored.
>
> I've gotten more than one bug report about mkfs.{xfs,ext4} or nvml
> failing that were eventually tracked down to be wrong values passed to
> memmap.
>
> This patch prevents the above issue by instead of adding a new memory
> range, only update a RAM memory range with the PRAM type. This way,
> passing the wrong memmap will either not give you a pmem at all or give
> you a smaller one that actually has RAM behind it.
>
> And if someone still needs to fake a pmem that doesn't have RAM behind
> it, they can simply do memmap=XX@YY,XX!YY.
>
> Signed-off-by: Yigal Korman <yigal@plexistor.com>

Acked-by: Dan Williams <dan.j.williams@intel.com>

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#1427763

On Mon, Jun 20, 2016 at 10:33:59AM +0300, Yigal Korman wrote:
> Before this patch, passing a range that is beyond the physical memory
> range will succeed, the user will see a /dev/pmem0 and will be able to
> access it. Reads will always return 0 and writes will be silently
> ignored.
> 
> I've gotten more than one bug report about mkfs.{xfs,ext4} or nvml
> failing that were eventually tracked down to be wrong values passed to
> memmap.
> 
> This patch prevents the above issue by instead of adding a new memory
> range, only update a RAM memory range with the PRAM type. This way,
> passing the wrong memmap will either not give you a pmem at all or give
> you a smaller one that actually has RAM behind it.
> 
> And if someone still needs to fake a pmem that doesn't have RAM behind
> it, they can simply do memmap=XX@YY,XX!YY.
> 
> Signed-off-by: Yigal Korman <yigal@plexistor.com>

Acked-by: Johannes Thumshirn <jthumshirn@suse.de>

-- 
Johannes Thumshirn                                          Storage
jthumshirn@suse.de                                +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850

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#1429732

On 06/20/2016 10:33 AM, Yigal Korman wrote:
> Before this patch, passing a range that is beyond the physical memory
> range will succeed, the user will see a /dev/pmem0 and will be able to
> access it. Reads will always return 0 and writes will be silently
> ignored.
> 
> I've gotten more than one bug report about mkfs.{xfs,ext4} or nvml
> failing that were eventually tracked down to be wrong values passed to
> memmap.
> 
> This patch prevents the above issue by instead of adding a new memory
> range, only update a RAM memory range with the PRAM type. This way,
> passing the wrong memmap will either not give you a pmem at all or give
> you a smaller one that actually has RAM behind it.
> 
> And if someone still needs to fake a pmem that doesn't have RAM behind
> it, they can simply do memmap=XX@YY,XX!YY.
> 

We are running with this patch for a while in the lab and it does
solve the problem above with no maleffects so:

Tested-by: Boaz Harrosh <boaz@plexistor.com>

> Signed-off-by: Yigal Korman <yigal@plexistor.com>
> ---
>  arch/x86/kernel/e820.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index 621b501..4bd4207 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -878,7 +878,7 @@ static int __init parse_memmap_one(char *p)
>  		e820_add_region(start_at, mem_size, E820_RESERVED);
>  	} else if (*p == '!') {
>  		start_at = memparse(p+1, &p);
> -		e820_add_region(start_at, mem_size, E820_PRAM);
> +		e820_update_range(start_at, mem_size, E820_RAM, E820_PRAM);
>  	} else
>  		e820_remove_range(mem_size, ULLONG_MAX - mem_size, E820_RAM, 1);
>  
> 

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