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Re: [Xen-devel] [PATCHv4 18/33] x86/xen: convert __xen_pgd_walk() and xen_cleanmfnmap() to support p4d

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On 03/07/2017 01:26 PM, Andrew Cooper wrote:
> On 07/03/17 18:18, Boris Ostrovsky wrote:
>>>> Don't we need to pass vaddr down to all routines so that they select
>>>> appropriate tables? You seem to always be choosing the first one.
>>> IIUC, we clear whole page table subtree covered by one pgd entry.
>>> So, no, there's no need to pass vaddr down. Just pointer to page table
>>> entry is enough.
>>>
>>> But I know virtually nothing about Xen. Please re-check my reasoning.
>> Yes, we effectively remove the whole page table for vaddr so I guess
>> it's OK.
>>
>>> I would also appreciate help with getting x86 Xen code work with 5-level
>>> paging enabled. For now I make CONFIG_XEN dependent on !CONFIG_X86_5LEVEL.
>> Hmmm... that's a problem since this requires changes in the hypervisor
>> and even if/when these changes are made older version of hypervisor
>> still will not be able to run those guests.
>>
>> This affects only PV guests and there is a series under review that
>> provides clean code separation with CONFIG_XEN_PV but because, for
>> example, dom0 (Xen control domain) is PV this will significantly limit
>> availability of dom0-capable kernels (because I assume distros will want
>> to have CONFIG_X86_5LEVEL).
> Wasn't the plan to be able to automatically detect 4 vs 5 level support,
> and cope either way, so distros didn't have to ship two different builds
> of Linux?
>
> If so, all we need to do git things to compile sensibly, and have the PV
> entry code in Linux configure the rest of the kernel appropriately.

I am not aware of any plans but this would obviously be the preferred route.

-boris

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[PATCHv4 00/33] 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 01/33] x86/cpufeature: Add 5-level paging detection "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 14/33] x86/kexec: support p4d_t "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 18/33] x86/xen: convert __xen_pgd_walk() and xen_cleanmfnmap() to support p4d "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
    Re: [PATCHv4 18/33] x86/xen: convert __xen_pgd_walk() and  xen_cleanmfnmap() to support p4d Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2017-03-06 21:50 +0100
      Re: [PATCHv4 18/33] x86/xen: convert __xen_pgd_walk() and  xen_cleanmfnmap() to support p4d "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-03-07 14:10 +0100
        Re: [PATCHv4 18/33] x86/xen: convert __xen_pgd_walk() and  xen_cleanmfnmap() to support p4d Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2017-03-07 19:20 +0100
          Re: [Xen-devel] [PATCHv4 18/33] x86/xen: convert __xen_pgd_walk() and  xen_cleanmfnmap() to support p4d Andrew Cooper <andrew.cooper3@citrix.com> - 2017-03-07 19:30 +0100
            Re: [Xen-devel] [PATCHv4 18/33] x86/xen: convert __xen_pgd_walk() and  xen_cleanmfnmap() to support p4d Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2017-03-07 20:30 +0100
  [PATCHv4 30/33] x86/mm: make kernel_physical_mapping_init() support 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 21/33] x86/asm: remove __VIRTUAL_MASK_SHIFT==47 assert "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 08/33] x86: basic changes into headers for 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 16/33] x86/mm/pat: handle additional page table "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 05/33] asm-generic: introduce <asm-generic/pgtable-nop4d.h> "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 15/33] x86/efi: handle p4d in EFI pagetables "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 19/33] x86: convert the rest of the code to support p4d_t "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 20/33] x86: detect 5-level paging support "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 07/33] mm: introduce __p4d_alloc() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 27/33] x86/espfix: support 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 13/33] x86/power: support p4d_t in hibernate code "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:10 +0100
  [PATCHv4 02/33] asm-generic: introduce 5level-fixup.h "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-06 15:20 +0100
  Re: [PATCHv4 00/33] 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-06 19:40 +0100
    Re: [PATCHv4 00/33] 5-level paging Thomas Gleixner <tglx@linutronix.de> - 2017-03-06 19:50 +0100
      Re: [PATCHv4 00/33] 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-06 20:10 +0100
        Re: [PATCHv4 00/33] 5-level paging "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-03-06 20:10 +0100
          Re: [PATCHv4 00/33] 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-06 20:50 +0100
      Re: [PATCHv4 00/33] 5-level paging Stephen Rothwell <sfr@canb.auug.org.au> - 2017-03-07 02:30 +0100
        Re: [PATCHv4 00/33] 5-level paging Thomas Gleixner <tglx@linutronix.de> - 2017-03-07 11:20 +0100

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