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From: Dave Hansen <dave.hansen@linux.intel.com>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	luto@kernel.org, torvalds@linux-foundation.org,
	keescook@google.com, hughd@google.com, jgross@suse.com,
	x86@kernel.org
Subject: Re: [PATCH 2/3] x86/mm: introduce __PAGE_KERNEL_GLOBAL
Date: Fri, 16 Feb 2018 11:06:30 -0800	[thread overview]
Message-ID: <0f8abc68-1092-1bae-d244-1adbbee455f9@linux.intel.com> (raw)
In-Reply-To: <DF43D1DD-42EE-4545-9F54-4BC2395D66EA@gmail.com>

On 02/16/2018 10:25 AM, Nadav Amit wrote:
>> +#ifdef CONFIG_PAGE_TABLE_ISOLATION
>> +#define __PAGE_KERNEL_GLOBAL		0
>> +#else
>> +#define __PAGE_KERNEL_GLOBAL		_PAGE_GLOBAL
>> +#endif
> ...
>> --- a/arch/x86/mm/pageattr.c~kpti-no-global-for-kernel-mappings	2018-02-13 15:17:56.148210060 -0800
>> +++ b/arch/x86/mm/pageattr.c	2018-02-13 15:17:56.153210060 -0800
>> @@ -593,7 +593,8 @@ try_preserve_large_page(pte_t *kpte, uns
>> 	 * different bit positions in the two formats.
>> 	 */
>> 	req_prot = pgprot_4k_2_large(req_prot);
>> -	req_prot = pgprot_set_on_present(req_prot, _PAGE_GLOBAL | _PAGE_PSE);
>> +	req_prot = pgprot_set_on_present(req_prot,
>> +			__PAGE_KERNEL_GLOBAL | _PAGE_PSE);
>> 	req_prot = canon_pgprot(req_prot);
> From these chunks, it seems to me as req_prot will not have the global bit
> on when “nopti” parameter is provided. What am I missing?

That's a good point.  The current patch does not allow the use of
_PAGE_GLOBAL via _PAGE_KERNEL_GLOBAL when CONFIG_PAGE_TABLE_ISOLATION=y,
but booted with nopti.  It's a simple enough fix.  Logically:

#ifdef CONFIG_PAGE_TABLE_ISOLATION
#define __PAGE_KERNEL_GLOBAL	static_cpu_has(X86_FEATURE_PTI) ?
					0 : _PAGE_GLOBAL
#else
#define __PAGE_KERNEL_GLOBAL	_PAGE_GLOBAL
#endif

But I don't really want to hide that gunk in a macro like that.  It
might make more sense as a static inline.  I'll give that a shot and resent.

WARNING: multiple messages have this Message-ID (diff)
From: Dave Hansen <dave.hansen@linux.intel.com>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	luto@kernel.org, torvalds@linux-foundation.org,
	keescook@google.com, hughd@google.com, jgross@suse.com,
	x86@kernel.org
Subject: Re: [PATCH 2/3] x86/mm: introduce __PAGE_KERNEL_GLOBAL
Date: Fri, 16 Feb 2018 11:06:30 -0800	[thread overview]
Message-ID: <0f8abc68-1092-1bae-d244-1adbbee455f9@linux.intel.com> (raw)
In-Reply-To: <DF43D1DD-42EE-4545-9F54-4BC2395D66EA@gmail.com>

On 02/16/2018 10:25 AM, Nadav Amit wrote:
>> +#ifdef CONFIG_PAGE_TABLE_ISOLATION
>> +#define __PAGE_KERNEL_GLOBAL		0
>> +#else
>> +#define __PAGE_KERNEL_GLOBAL		_PAGE_GLOBAL
>> +#endif
> ...
>> --- a/arch/x86/mm/pageattr.c~kpti-no-global-for-kernel-mappings	2018-02-13 15:17:56.148210060 -0800
>> +++ b/arch/x86/mm/pageattr.c	2018-02-13 15:17:56.153210060 -0800
>> @@ -593,7 +593,8 @@ try_preserve_large_page(pte_t *kpte, uns
>> 	 * different bit positions in the two formats.
>> 	 */
>> 	req_prot = pgprot_4k_2_large(req_prot);
>> -	req_prot = pgprot_set_on_present(req_prot, _PAGE_GLOBAL | _PAGE_PSE);
>> +	req_prot = pgprot_set_on_present(req_prot,
>> +			__PAGE_KERNEL_GLOBAL | _PAGE_PSE);
>> 	req_prot = canon_pgprot(req_prot);
> From these chunks, it seems to me as req_prot will not have the global bit
> on when a??noptia?? parameter is provided. What am I missing?

That's a good point.  The current patch does not allow the use of
_PAGE_GLOBAL via _PAGE_KERNEL_GLOBAL when CONFIG_PAGE_TABLE_ISOLATION=y,
but booted with nopti.  It's a simple enough fix.  Logically:

#ifdef CONFIG_PAGE_TABLE_ISOLATION
#define __PAGE_KERNEL_GLOBAL	static_cpu_has(X86_FEATURE_PTI) ?
					0 : _PAGE_GLOBAL
#else
#define __PAGE_KERNEL_GLOBAL	_PAGE_GLOBAL
#endif

But I don't really want to hide that gunk in a macro like that.  It
might make more sense as a static inline.  I'll give that a shot and resent.

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  reply	other threads:[~2018-02-16 19:06 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-15 13:20 [PATCH 0/3] Use global pages with PTI Dave Hansen
2018-02-15 13:20 ` Dave Hansen
2018-02-15 13:20 ` [PATCH 1/3] x86/mm: factor out conditional pageattr PTE bit setting code Dave Hansen
2018-02-15 13:20   ` Dave Hansen
2018-02-15 13:20 ` [PATCH 2/3] x86/mm: introduce __PAGE_KERNEL_GLOBAL Dave Hansen
2018-02-15 13:20   ` Dave Hansen
2018-02-16 17:47   ` Nadav Amit
2018-02-16 17:47     ` Nadav Amit
2018-02-16 18:03     ` Dave Hansen
2018-02-16 18:03       ` Dave Hansen
2018-02-16 18:25       ` Nadav Amit
2018-02-16 18:25         ` Nadav Amit
2018-02-16 19:06         ` Dave Hansen [this message]
2018-02-16 19:06           ` Dave Hansen
2018-02-16 19:54           ` Nadav Amit
2018-02-16 19:54             ` Nadav Amit
2018-02-16 20:00             ` Dave Hansen
2018-02-16 20:00               ` Dave Hansen
2018-02-16 23:19         ` Dave Hansen
2018-02-16 23:19           ` Dave Hansen
2018-02-15 13:20 ` [PATCH 3/3] x86/pti: enable global pages for shared areas Dave Hansen
2018-02-15 13:20   ` Dave Hansen
2018-02-15 17:47 ` [PATCH 0/3] Use global pages with PTI Linus Torvalds
2018-02-15 17:47   ` Linus Torvalds
2018-02-15 18:13   ` Dave Hansen
2018-02-15 18:13     ` Dave Hansen
2018-02-15 23:55   ` Dave Hansen
2018-02-15 23:55     ` Dave Hansen
  -- strict thread matches above, loose matches on Subject: below --
2018-02-13 23:19 Dave Hansen
2018-02-13 23:19 ` [PATCH 2/3] x86/mm: introduce __PAGE_KERNEL_GLOBAL Dave Hansen

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