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From: Dave Hansen <dave.hansen@intel.com>
To: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Tianyu Lan <Tianyu.Lan@microsoft.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, vbabka@suse.cz,
	akpm@linux-foundation.org, willy@infradead.org
Subject: Re: Is _PAGE_PROTNONE set only for user mappings?
Date: Thu, 2 Jun 2022 09:47:33 -0700	[thread overview]
Message-ID: <1f0fd9f4-295f-6b44-47ff-b6b56892e680@intel.com> (raw)
In-Reply-To: <YpNLxXvGFQpyPjRa@n2.us-central1-a.c.spheric-algebra-350919.internal>

On 5/29/22 03:32, Hyeonggon Yoo wrote:
> On Mon, May 16, 2022 at 07:04:32AM -0700, Dave Hansen wrote:
> Writing code I'm a bit confused:
> commit d1440b23c922d8 ("x86/mm: Factor out pageattr
> _PAGE_GLOBAL setting") says:
> 
> 	"This unconditional setting of _PAGE_GLOBAL is a problem when we have
> 	PTI and non-PTI and we want some areas to have _PAGE_GLOBAL and some
> 	not." 
> 
> Is this this sentence not valid anymore in PTI,
> and just unconditionally setting _PAGE_GLOBAL would be okay in kernel
> side regardless of PTI?

I believe it's still valid.

IIRC, there are three cases:

1. No KPTI.  All kernel mappings are _PAGE_GLOBAL.  Basically, for
   present mappings, if _PAGE_USER is clear, _PAGE_GLOBAL is set.
2. KPTI with PCID hardware support (or in a few other cases): The kernel
   image is mostly non-global.  Anything mapped into userspace *is*
   marked global, like entry text.
3. KPTI without PCIDs: Basically case #2, but with more of the kernel
   image left global.

So, not only are there different KPTI modes, there a different pars of
the kernel that require different _PAGE_GLOBAL behavior.

pti_kernel_image_global_ok() in arch/x86/mm/pti.c explains it pretty well.

  reply	other threads:[~2022-06-02 16:47 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-06  5:19 [PATCH] x86/mm/cpa: set PAGE_KERNEL in __set_pages_p() Hyeonggon Yoo
2022-05-09 16:06 ` Tom Lendacky
2022-05-10 11:57   ` Hyeonggon Yoo
2022-05-10 13:35     ` Tom Lendacky
2022-05-10 14:39       ` Dave Hansen
2022-05-11  5:20         ` Is _PAGE_PROTNONE set only for user mappings? Hyeonggon Yoo
2022-05-12 10:37           ` Mel Gorman
2022-05-13  5:33             ` Hyeonggon Yoo
2022-05-16 13:03               ` Mel Gorman
2022-05-16 14:04               ` Dave Hansen
2022-05-22  3:56                 ` Hyeonggon Yoo
2022-05-24 20:22                   ` Sean Christopherson
2022-05-26 10:33                     ` Hyeonggon Yoo
2022-05-29 10:32                 ` Hyeonggon Yoo
2022-06-02 16:47                   ` Dave Hansen [this message]
2022-05-10  0:47 ` [PATCH] x86/mm/cpa: set PAGE_KERNEL in __set_pages_p() Edgecombe, Rick P
2022-05-10 11:50   ` Hyeonggon Yoo
2022-05-10 15:38     ` Edgecombe, Rick P

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