From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Ingo Molnar <mingo@kernel.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@amacapital.net>,
Cyrill Gorcunov <gorcunov@openvz.org>,
Borislav Petkov <bp@suse.de>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv7 12/19] x86/mm: Adjust virtual address space layout in early boot.
Date: Thu, 28 Sep 2017 17:28:09 +0300 [thread overview]
Message-ID: <20170928142809.3ste5znjtjmucwig@node.shutemov.name> (raw)
In-Reply-To: <20170928133838.oa72tybvmyy3sfgw@gmail.com>
On Thu, Sep 28, 2017 at 03:38:38PM +0200, Ingo Molnar wrote:
>
> * Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> > On Thu, Sep 28, 2017 at 10:31:55AM +0200, Ingo Molnar wrote:
> > >
> > > * Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote:
> > >
> > > > We need to adjust virtual address space to support switching between
> > > > paging modes.
> > > >
> > > > The adjustment happens in __startup_64().
> > >
> > > > +#ifdef CONFIG_X86_5LEVEL
> > > > + if (__read_cr4() & X86_CR4_LA57) {
> > > > + pgtable_l5_enabled = 1;
> > > > + pgdir_shift = 48;
> > > > + ptrs_per_p4d = 512;
> > > > + }
> > > > +#endif
> > >
> > > So CR4 really sucks as a parameter passing interface - was it us who enabled LA57
> > > in the early boot code, right? Couldn't we add a flag which gets set there, or
> > > something?
> >
> > It's not necessary that we enabled LA57. At least I tried to write code
> > that doesn't assume this. We enable it if bootloader haven't done this
> > already for us.
> >
> > What is so awful about using CR4 as passing interface? It's one-time
> > check, so performance shouldn't be an issue.
>
> As a starter, this code is in generic x86 code [choose_random_location()], is this
> CR4 bit known to AMD as well and is it guaranteed to be sane across all x86 CPUs?
> I don't think so.
It's architectural thing, so it's consistent across all x86
implementations.
> CR4 is a poor interface to pass CPU features through. Generaly we try to enumerate
> CPU features via CPUID, and/or enable synthetic CPU features in certain cases, and
> work from there.
Okay, has_cpuflag(X86_FEATURE_LA57) seems would do.
--
Kirill A. Shutemov
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next prev parent reply other threads:[~2017-09-28 14:28 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-18 10:55 [PATCHv7 00/19] Boot-time switching between 4- and 5-level paging for 4.15 Kirill A. Shutemov
2017-09-18 10:55 ` [PATCHv7 01/19] mm/sparsemem: Allocate mem_section at runtime for SPARSEMEM_EXTREME Kirill A. Shutemov
2017-09-28 8:07 ` Ingo Molnar
2017-09-28 9:08 ` Kirill A. Shutemov
2017-09-28 9:39 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 02/19] mm/zsmalloc: Prepare to variable MAX_PHYSMEM_BITS Kirill A. Shutemov
2017-09-28 8:10 ` Ingo Molnar
2017-09-28 9:19 ` Kirill A. Shutemov
2017-09-28 9:44 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 03/19] x86/kasan: Use the same shadow offset for 4- and 5-level paging Kirill A. Shutemov
2017-09-28 8:15 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 04/19] x86/xen: Provide pre-built page tables only for XEN_PV and XEN_PVH Kirill A. Shutemov
2017-09-18 10:55 ` [PATCHv7 05/19] x86/xen: Drop 5-level paging support code from XEN_PV code Kirill A. Shutemov
2017-09-18 10:55 ` [PATCHv7 06/19] x86/boot/compressed/64: Detect and handle 5-level paging at boot-time Kirill A. Shutemov
2017-09-28 8:18 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 07/19] x86/mm: Make virtual memory layout movable for CONFIG_X86_5LEVEL Kirill A. Shutemov
2017-09-28 8:19 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 08/19] x86/mm: Make PGDIR_SHIFT and PTRS_PER_P4D variable Kirill A. Shutemov
2017-09-19 14:03 ` Kirill A. Shutemov
2017-09-28 8:21 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 09/19] x86/mm: Make MAX_PHYSADDR_BITS and MAX_PHYSMEM_BITS dynamic Kirill A. Shutemov
2017-09-28 8:25 ` Ingo Molnar
2017-09-28 10:17 ` Kirill A. Shutemov
2017-09-28 10:40 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 10/19] x86/mm: Make __PHYSICAL_MASK_SHIFT and __VIRTUAL_MASK_SHIFT dynamic Kirill A. Shutemov
2017-09-28 8:28 ` Ingo Molnar
2017-09-28 10:22 ` Kirill A. Shutemov
2017-09-28 10:42 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 11/19] x86/mm: Make STACK_TOP_MAX dynamic Kirill A. Shutemov
2017-09-28 8:29 ` Ingo Molnar
2017-09-28 13:19 ` Kirill A. Shutemov
2017-09-18 10:55 ` [PATCHv7 12/19] x86/mm: Adjust virtual address space layout in early boot Kirill A. Shutemov
2017-09-28 8:31 ` Ingo Molnar
2017-09-28 13:26 ` Kirill A. Shutemov
2017-09-28 13:38 ` Ingo Molnar
2017-09-28 14:28 ` Kirill A. Shutemov [this message]
2017-09-18 10:55 ` [PATCHv7 13/19] x86/mm: Make early boot code support boot-time switching of paging modes Kirill A. Shutemov
2017-09-28 8:33 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 14/19] x86/mm: Fold p4d page table layer at runtime Kirill A. Shutemov
2017-09-18 10:55 ` [PATCHv7 15/19] x86/mm: Replace compile-time checks for 5-level with runtime-time Kirill A. Shutemov
2017-09-28 8:35 ` Ingo Molnar
2017-09-18 10:55 ` [PATCHv7 16/19] x86/mm: Allow to boot without la57 if CONFIG_X86_5LEVEL=y Kirill A. Shutemov
2017-09-18 10:55 ` [PATCHv7 17/19] x86/xen: Allow XEN_PV and XEN_PVH to be enabled with X86_5LEVEL Kirill A. Shutemov
2017-09-18 10:55 ` [PATCHv7 18/19] x86/mm: Redefine some of page table helpers as macros Kirill A. Shutemov
2017-09-18 10:55 ` [PATCHv7 19/19] x86/mm: Offset boot-time paging mode switching cost Kirill A. Shutemov
2017-09-25 13:16 ` [PATCHv7 00/19] Boot-time switching between 4- and 5-level paging for 4.15 Kirill A. Shutemov
2017-09-28 8:36 ` Ingo Molnar
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