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From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
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	linux-mm@kvack.org, Paul Mackerras <paulus@samba.org>,
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	Steven Price <Steven.Price@arm.com>,
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	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Vineet Gupta <vgupta@synopsys.com>,
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	Andrew Morton <akpm@linux-foundation.org>,
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	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers
Date: Thu, 13 Feb 2020 07:45:55 +0530
Message-ID: <085cdec7-1759-82c6-7a65-9b7d28c1c458@arm.com> (raw)
In-Reply-To: <20200212185548.3274ec2e@thinkpad>



On 02/12/2020 11:25 PM, Gerald Schaefer wrote:
> On Wed, 12 Feb 2020 15:12:54 +0530
> Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> 
>>>> +/*
>>>> + * On s390 platform, the lower 12 bits are used to identify given page table
>>>> + * entry type and for other arch specific requirements. But these bits might
>>>> + * affect the ability to clear entries with pxx_clear(). So while loading up
>>>> + * the entries skip all lower 12 bits in order to accommodate s390 platform.
>>>> + * It does not have affect any other platform.
>>>> + */
>>>> +#define RANDOM_ORVALUE	(0xfffffffffffff000UL)  
>>>
>>> I'd suggest you generate this mask with something like
>>> GENMASK(BITS_PER_LONG, PAGE_SHIFT).  
>>
>> IIRC the lower 12 bits constrains on s390 platform might not be really related
>> to it's PAGE_SHIFT which can be a variable, but instead just a constant number.
>> But can definitely use GENMASK or it's variants here.
>>
>> https://lkml.org/lkml/2019/9/5/862
> 
> PAGE_SHIFT would be fine, it is 12 on s390. However, in order to be
> more precise, we do not really need all 12 bits, only the last 4 bits.
> So, something like this would work:
> 
> #define RANDOM_ORVALUE GENMASK(BITS_PER_LONG - 1, 4)
> 
> The text in the comment could then also be changed from 12 to 4, and
> be a bit more specific on the fact that the impact on pxx_clear()
> results from the dynamic page table folding logic on s390:
> 
> /*
>  * On s390 platform, the lower 4 bits are used to identify given page table
>  * entry type. But these bits might affect the ability to clear entries with
>  * pxx_clear() because of how dynamic page table folding works on s390. So
>  * while loading up the entries do not change the lower 4 bits.
>  * It does not have affect any other platform.
>  */

Sure, will update accordingly.

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Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-28  1:27 Anshuman Khandual
2020-01-28  2:11 ` Qian Cai
2020-01-28  3:06   ` Anshuman Khandual
2020-01-28  3:33     ` Qian Cai
2020-01-28  4:57       ` Anshuman Khandual
2020-01-28  5:48         ` Qian Cai
2020-01-28  6:17           ` Christophe Leroy
2020-01-28  6:36             ` Qian Cai
2020-01-28  7:03               ` Anshuman Khandual
2020-01-28  7:07                 ` Qian Cai
2020-01-28  6:13       ` Christophe Leroy
2020-01-28  7:12         ` Qian Cai
2020-01-28 11:58           ` Mark Brown
2020-01-28 12:09       ` Mike Rapoport
2020-01-28 17:14       ` Vineet Gupta
2020-01-29 22:20       ` Gerald Schaefer
2020-01-30  7:27         ` Mike Rapoport
2020-01-30 13:32           ` Anshuman Khandual
2020-01-28 17:47   ` Catalin Marinas
2020-01-28 19:07     ` Qian Cai
2020-01-29 10:36       ` Catalin Marinas
2020-01-29 11:09         ` Qian Cai
2020-01-28 17:05 ` Christophe Leroy
2020-01-30 13:04   ` Anshuman Khandual
2020-01-30 14:13     ` Christophe Leroy
2020-02-02  7:18       ` Anshuman Khandual
2020-02-02  8:31         ` Christophe Leroy
2020-02-02 11:26       ` Qian Cai
2020-02-03 15:14         ` Christophe Leroy
2020-02-03 15:48           ` Qian Cai
2020-02-02  8:26     ` Anshuman Khandual
2020-01-29 22:20 ` Gerald Schaefer
2020-01-30 13:11   ` Anshuman Khandual
2020-01-30 15:06 ` Anshuman Khandual
2020-02-10 15:37 ` Catalin Marinas
2020-02-12  9:42   ` Anshuman Khandual
2020-02-12 17:55     ` Gerald Schaefer
2020-02-13  2:15       ` Anshuman Khandual [this message]

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