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    Subject[PATCH v4 11/12] x86/mtrr: don't let mtrr_type_lookup() return MTRR_TYPE_INVALID
    Date
    mtrr_type_lookup() should always return a valid memory type. In case
    there is no information available, it should return the default UC.

    This will remove the last case where mtrr_type_lookup() can return
    MTRR_TYPE_INVALID, so adjust the comment in include/uapi/asm/mtrr.h.

    Note that removing the MTRR_TYPE_INVALID #define from that header
    could break user code, so it has to stay.

    At the same time the mtrr_type_lookup() stub for the !CONFIG_MTRR
    case should set uniform to 1, as if the memory range would be
    covered by no MTRR at all.

    Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Juergen Gross <jgross@suse.com>
    ---
    V2:
    - always set uniform
    - set uniform to 1 in case of disabled MTRRs (Linus Torvalds)
    V3:
    - adjust include/uapi/asm/mtrr.h comment
    ---
    arch/x86/include/asm/mtrr.h | 7 +++++--
    arch/x86/include/uapi/asm/mtrr.h | 6 +++---
    arch/x86/kernel/cpu/mtrr/generic.c | 4 ++--
    3 files changed, 10 insertions(+), 7 deletions(-)

    diff --git a/arch/x86/include/asm/mtrr.h b/arch/x86/include/asm/mtrr.h
    index f1cb81330a64..0d7ea8a54d81 100644
    --- a/arch/x86/include/asm/mtrr.h
    +++ b/arch/x86/include/asm/mtrr.h
    @@ -59,9 +59,12 @@ static inline void mtrr_overwrite_state(struct mtrr_var_range *var,
    static inline u8 mtrr_type_lookup(u64 addr, u64 end, u8 *uniform)
    {
    /*
    - * Return no-MTRRs:
    + * Return the default MTRR type, without any known other types in
    + * that range.
    */
    - return MTRR_TYPE_INVALID;
    + *uniform = 1;
    +
    + return MTRR_TYPE_UNCACHABLE;
    }
    #define mtrr_save_fixed_ranges(arg) do {} while (0)
    #define mtrr_save_state() do {} while (0)
    diff --git a/arch/x86/include/uapi/asm/mtrr.h b/arch/x86/include/uapi/asm/mtrr.h
    index 376563f2bac1..4aa05c2ffa78 100644
    --- a/arch/x86/include/uapi/asm/mtrr.h
    +++ b/arch/x86/include/uapi/asm/mtrr.h
    @@ -115,9 +115,9 @@ struct mtrr_state_type {
    #define MTRR_NUM_TYPES 7

    /*
    - * Invalid MTRR memory type. mtrr_type_lookup() returns this value when
    - * MTRRs are disabled. Note, this value is allocated from the reserved
    - * values (0x7-0xff) of the MTRR memory types.
    + * Invalid MTRR memory type. No longer used outside of MTRR code.
    + * Note, this value is allocated from the reserved values (0x7-0xff) of
    + * the MTRR memory types.
    */
    #define MTRR_TYPE_INVALID 0xff

    diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
    index de6d74d6e3a0..3d48e9d06bfb 100644
    --- a/arch/x86/kernel/cpu/mtrr/generic.c
    +++ b/arch/x86/kernel/cpu/mtrr/generic.c
    @@ -417,13 +417,13 @@ u8 mtrr_type_lookup(u64 start, u64 end, u8 *uniform)

    if (!mtrr_state_set) {
    *uniform = 0; /* Uniformity is unknown. */
    - return MTRR_TYPE_INVALID;
    + return MTRR_TYPE_UNCACHABLE;
    }

    *uniform = 1;

    if (!(mtrr_state.enabled & MTRR_STATE_MTRR_ENABLED))
    - return MTRR_TYPE_INVALID;
    + return MTRR_TYPE_UNCACHABLE;

    for (i = 0; i < cache_map_n && start < end; i++) {
    if (start >= cache_map[i].end)
    --
    2.35.3
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