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    SubjectRe: [PATCH v2] X86: don't report PAT on CPUs that don't support it
    On Mon, 3 Jul 2017, Mikulas Patocka wrote:
    > Is there any progress with this patch? Will you accept it or do you want
    > some changes to it?

    Aside of the unparseable changelog, that patch is mostly duct tape.

    1) __pat_enabled should be renamed to pat_disabled, as that is the actual
    purpose of that variable

    2) Making the call to init_cache_modes() conditional in setup_arch() is
    pointless. init_cache_modes() has it's own protection against multiple
    invocations.

    3) It adds yet another invocation of init_cache_modes() instead of getting
    rid of the ones in pat_disable() and the pat disabled case in pat_init().

    I've reworked the whole thing into the patch below.

    Thanks,

    tglx

    8<---------------------
    Subject: x86/mm/pat: Don't report PAT on CPUs that don't support it
    From: Mikulas Patocka <mpatocka@redhat.com>
    Date: Tue, 6 Jun 2017 18:49:39 -0400 (EDT)

    The pat_enabled() logic is broken on CPUs which do not support PAT and
    where the initialization code fails to call pat_init(). Due to that the
    enabled flag stays true and pat_enabled() returns true wrongfully.

    As a consequence the mappings, e.g. for Xorg, are set up with the wrong
    caching mode and the required MTRR setups are omitted.

    To cure this the following changes are required:

    1) Make pat_enabled() return true only if PAT initialization was
    invoked and successful.

    2) Invoke init_cache_modes() unconditionally in setup_arch() and
    remove the extra callsites in pat_disable() and the pat disabled
    code path in pat_init().

    Also rename __pat_enabled to pat_disabled to reflect the real purpose of
    this variable.

    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
    Cc: Bernhard Held <berny156@gmx.de>
    Cc: Toshi Kani <toshi.kani@hp.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: "Luis R. Rodriguez" <mcgrof@suse.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>

    ---
    arch/x86/include/asm/pat.h | 1 +
    arch/x86/kernel/setup.c | 7 +++++++
    arch/x86/mm/pat.c | 22 +++++++++-------------
    3 files changed, 17 insertions(+), 13 deletions(-)

    --- a/arch/x86/include/asm/pat.h
    +++ b/arch/x86/include/asm/pat.h
    @@ -7,6 +7,7 @@
    bool pat_enabled(void);
    void pat_disable(const char *reason);
    extern void pat_init(void);
    +extern void init_cache_modes(void);

    extern int reserve_memtype(u64 start, u64 end,
    enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
    --- a/arch/x86/kernel/setup.c
    +++ b/arch/x86/kernel/setup.c
    @@ -1076,6 +1076,13 @@ void __init setup_arch(char **cmdline_p)
    max_possible_pfn = max_pfn;

    /*
    + * This call is required when the CPU does not support PAT. If
    + * mtrr_bp_init() invoked it already via pat_init() the call has no
    + * effect.
    + */
    + init_cache_modes();
    +
    + /*
    * Define random base addresses for memory sections after max_pfn is
    * defined and before each memory section base is used.
    */
    --- a/arch/x86/mm/pat.c
    +++ b/arch/x86/mm/pat.c
    @@ -37,14 +37,13 @@
    #undef pr_fmt
    #define pr_fmt(fmt) "" fmt

    -static bool boot_cpu_done;
    -
    -static int __read_mostly __pat_enabled = IS_ENABLED(CONFIG_X86_PAT);
    -static void init_cache_modes(void);
    +static bool __read_mostly boot_cpu_done;
    +static bool __read_mostly pat_disabled = !IS_ENABLED(CONFIG_X86_PAT);
    +static bool __read_mostly pat_initialized;

    void pat_disable(const char *reason)
    {
    - if (!__pat_enabled)
    + if (pat_disabled)
    return;

    if (boot_cpu_done) {
    @@ -52,10 +51,8 @@ void pat_disable(const char *reason)
    return;
    }

    - __pat_enabled = 0;
    + pat_disabled = true;
    pr_info("x86/PAT: %s\n", reason);
    -
    - init_cache_modes();
    }

    static int __init nopat(char *str)
    @@ -67,7 +64,7 @@ early_param("nopat", nopat);

    bool pat_enabled(void)
    {
    - return !!__pat_enabled;
    + return pat_initialized;
    }
    EXPORT_SYMBOL_GPL(pat_enabled);

    @@ -225,6 +222,7 @@ static void pat_bsp_init(u64 pat)
    }

    wrmsrl(MSR_IA32_CR_PAT, pat);
    + __pat_initialized = true;

    __init_cache_modes(pat);
    }
    @@ -242,7 +240,7 @@ static void pat_ap_init(u64 pat)
    wrmsrl(MSR_IA32_CR_PAT, pat);
    }

    -static void init_cache_modes(void)
    +void init_cache_modes(void)
    {
    u64 pat = 0;
    static int init_cm_done;
    @@ -306,10 +304,8 @@ void pat_init(void)
    u64 pat;
    struct cpuinfo_x86 *c = &boot_cpu_data;

    - if (!pat_enabled()) {
    - init_cache_modes();
    + if (pat_disabled)
    return;
    - }

    if ((c->x86_vendor == X86_VENDOR_INTEL) &&
    (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||

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