From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
linux-mm@kvack.org, Mark Rutland <mark.rutland@arm.com>,
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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 [thread overview]
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.
next prev parent reply other threads:[~2020-02-13 2:16 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-28 1:27 [PATCH V12] mm/debug: Add tests validating architecture page table helpers 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
2020-01-29 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]
2020-01-28 12:30 Qian Cai
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