linux-kernel - Re: [PATCH 1/3] x86/xen: Allow XEN_PV and XEN_PVH to be enabled with X86

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Date:   Fri, 16 Feb 2018 18:00:13 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...e.de>, Andi Kleen <ak@...ux.intel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] x86/xen: Allow XEN_PV and XEN_PVH to be enabled with
 X86_5LEVEL

On Fri, Feb 16, 2018 at 06:11:10AM -0800, Matthew Wilcox wrote:
> On Fri, Feb 16, 2018 at 02:49:46PM +0300, Kirill A. Shutemov wrote:
> > @@ -38,12 +38,12 @@
> >   *
> >   */
> >  
> > +#define l4_index(x)	(((x) >> 39) & 511)
> >  #define pud_index(x)	(((x) >> PUD_SHIFT) & (PTRS_PER_PUD-1))
> 
> Shouldn't that be
> +#define p4d_index(x)	(((x) >> P4D_SHIFT) & (PTRS_PER_P4D-1))

With CONFIG_X86_5LEVEL=y, PTRS_PER_P4D is a varaible, so it won't compile.
With CONFIG_X86_5LEVEL=n, PTRS_PER_P4D is 1, so it's broken.

And I didn't want to mixin p4d here: it's actually top-level page table
in 4-level paging mode.

I guess we can do something like:

#define l4_index(x)	(((x) >> P4D_SIFT) & (PTRS_PER_PGD-1))

But to me it's more confusing than couple numbers.

-- 
 Kirill A. Shutemov