lkml.org 
[lkml]   [2022]   [Aug]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 5.19 109/158] x86/PAT: Have pat_enabled() properly reflect state when running on Xen
    Date
    From: Jan Beulich <jbeulich@suse.com>

    commit 72cbc8f04fe2fa93443c0fcccb7ad91dfea3d9ce upstream.

    After commit ID in the Fixes: tag, pat_enabled() returns false (because
    of PAT initialization being suppressed in the absence of MTRRs being
    announced to be available).

    This has become a problem: the i915 driver now fails to initialize when
    running PV on Xen (i915_gem_object_pin_map() is where I located the
    induced failure), and its error handling is flaky enough to (at least
    sometimes) result in a hung system.

    Yet even beyond that problem the keying of the use of WC mappings to
    pat_enabled() (see arch_can_pci_mmap_wc()) means that in particular
    graphics frame buffer accesses would have been quite a bit less optimal
    than possible.

    Arrange for the function to return true in such environments, without
    undermining the rest of PAT MSR management logic considering PAT to be
    disabled: specifically, no writes to the PAT MSR should occur.

    For the new boolean to live in .init.data, init_cache_modes() also needs
    moving to .init.text (where it could/should have lived already before).

    [ bp: This is the "small fix" variant for stable. It'll get replaced
    with a proper PAT and MTRR detection split upstream but that is too
    involved for a stable backport.
    - additional touchups to commit msg. Use cpu_feature_enabled(). ]

    Fixes: bdd8b6c98239 ("drm/i915: replace X86_FEATURE_PAT with pat_enabled()")
    Signed-off-by: Jan Beulich <jbeulich@suse.com>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Acked-by: Ingo Molnar <mingo@kernel.org>
    Cc: <stable@vger.kernel.org>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Lucas De Marchi <lucas.demarchi@intel.com>
    Link: https://lore.kernel.org/r/9385fa60-fa5d-f559-a137-6608408f88b0@suse.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/mm/pat/memtype.c | 10 +++++++++-
    1 file changed, 9 insertions(+), 1 deletion(-)

    --- a/arch/x86/mm/pat/memtype.c
    +++ b/arch/x86/mm/pat/memtype.c
    @@ -62,6 +62,7 @@

    static bool __read_mostly pat_bp_initialized;
    static bool __read_mostly pat_disabled = !IS_ENABLED(CONFIG_X86_PAT);
    +static bool __initdata pat_force_disabled = !IS_ENABLED(CONFIG_X86_PAT);
    static bool __read_mostly pat_bp_enabled;
    static bool __read_mostly pat_cm_initialized;

    @@ -86,6 +87,7 @@ void pat_disable(const char *msg_reason)
    static int __init nopat(char *str)
    {
    pat_disable("PAT support disabled via boot option.");
    + pat_force_disabled = true;
    return 0;
    }
    early_param("nopat", nopat);
    @@ -272,7 +274,7 @@ static void pat_ap_init(u64 pat)
    wrmsrl(MSR_IA32_CR_PAT, pat);
    }

    -void init_cache_modes(void)
    +void __init init_cache_modes(void)
    {
    u64 pat = 0;

    @@ -313,6 +315,12 @@ void init_cache_modes(void)
    */
    pat = PAT(0, WB) | PAT(1, WT) | PAT(2, UC_MINUS) | PAT(3, UC) |
    PAT(4, WB) | PAT(5, WT) | PAT(6, UC_MINUS) | PAT(7, UC);
    + } else if (!pat_force_disabled && cpu_feature_enabled(X86_FEATURE_HYPERVISOR)) {
    + /*
    + * Clearly PAT is enabled underneath. Allow pat_enabled() to
    + * reflect this.
    + */
    + pat_bp_enabled = true;
    }

    __init_cache_modes(pat);

    \
     
     \ /
      Last update: 2022-08-29 14:30    [W:2.708 / U:0.184 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site