linux-kernel - Re: [PATCH 1/4] x86/mm/pat: Handle no-GBPAGES case correctly in populate

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Message-ID: <CAKv+Gu-6YoJMLbR8UUsBeRPzk7r_4aKBprqay2kf6cKMPwsHgQ@mail.gmail.com>
Date:   Wed, 4 Mar 2020 20:04:04 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] x86/mm/pat: Handle no-GBPAGES case correctly in populate_pud

On Wed, 4 Mar 2020 at 19:50, Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> On Wed, Mar 04, 2020 at 07:44:50PM +0100, Ard Biesheuvel wrote:
> >
> > I've tried a couple of different ways, but I can't seem to get my
> > memory map organized in the way that will trigger the error.
>
> What does yours look like? efi_merge_regions doesn't merge everything
> that will eventually be mapped the same way, so if there are some
> non-conventional memory regions scattered over the address space, it
> might be breaking up the mappings to the point where this doesn't
> trigger.

I have a region

[    0.000000] efi: mem07: [Conventional Memory|   |  |  |  |  |  |  |
 |   |WB|WT|WC|UC] range=[0x0000000001400000-0x00000000b9855fff]
(2948MB)

which gets covered correctly

[    0.401766] 0x0000000000a00000-0x0000000040000000        1014M
RW         PSE         NX pmd
[    0.403436] 0x0000000040000000-0x0000000080000000           1G
RW         PSE         NX pud
[    0.404645] 0x0000000080000000-0x00000000b9800000         920M
RW         PSE         NX pmd
[    0.405844] 0x00000000b9800000-0x00000000b9a00000           2M
RW                     NX pte
[    0.407436] 0x00000000b9a00000-0x00000000baa00000          16M
ro         PSE         x  pmd
[    0.408591] 0x00000000baa00000-0x00000000bbe00000          20M
RW         PSE         NX pmd
[    0.409751] 0x00000000bbe00000-0x00000000bc000000           2M
RW                     NX pte
[    0.410821] 0x00000000bc000000-0x00000000be600000          38M
RW         PSE         NX pmd

However, the fact that you can provide a case where it does fail
should be sufficient justification for taking this patch. I was just
trying to give more than a regression-tested-by