From: Nadav Amit <nadav.amit@gmail.com>
To: Dave Hansen <dave.hansen@linux.intel.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 10:25:59 -0800 [thread overview]
Message-ID: <DF43D1DD-42EE-4545-9F54-4BC2395D66EA@gmail.com> (raw)
In-Reply-To: <a3dd1676-a2dc-aa02-77ad-51cd3b7a78d5@linux.intel.com>
Dave Hansen <dave.hansen@linux.intel.com> wrote:
> On 02/16/2018 09:47 AM, Nadav Amit wrote:
>>> But, this also means that we now get *no* opportunity to use
>>> global pages with PTI, even for data which is shared such as the
>>> cpu_entry_area and entry/exit text.
>>
>> Doesn’t this patch change the kernel behavior when the “nopti”
>> parameter is used?
>
> I don't think so. It takes the "nopti" behavior and effectively makes
> it apply everywhere. So it changes the PTI behavior, not the "nopti"
> behavior.
>
> Maybe it would help to quote the code that you think does this instead
> of the description. :)
Sorry, I thought it is obvious - so I must be missing something.
> +#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?
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next prev parent reply other threads:[~2018-02-16 18:26 UTC|newest]
Thread overview: 14+ 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 ` [PATCH 1/3] x86/mm: factor out conditional pageattr PTE bit setting code Dave Hansen
2018-02-15 13:20 ` [PATCH 2/3] x86/mm: introduce __PAGE_KERNEL_GLOBAL Dave Hansen
2018-02-16 17:47 ` Nadav Amit
2018-02-16 18:03 ` Dave Hansen
2018-02-16 18:25 ` Nadav Amit [this message]
2018-02-16 19:06 ` Dave Hansen
2018-02-16 19:54 ` Nadav Amit
2018-02-16 20:00 ` 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 17:47 ` [PATCH 0/3] Use global pages with PTI Linus Torvalds
2018-02-15 18:13 ` Dave Hansen
2018-02-15 23:55 ` Dave Hansen
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