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    SubjectRe: [RFC PATCH 4/6] ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on ASID-capable CPUs
    On 12/01/11 01:26, Catalin Marinas wrote:
    > On Thu, Dec 01, 2011 at 02:57:07AM +0000, Frank Rowand wrote:
    >> On 11/29/11 04:22, Catalin Marinas wrote:
    >>> Since the ASIDs must be unique to an mm across all the CPUs in a system,
    >>> the __new_context() function needs to broadcast a context reset event to
    >>> all the CPUs during ASID allocation if a roll-over occurred. Such IPIs
    >>> cannot be issued with interrupts disabled and ARM had to define
    >>> __ARCH_WANT_INTERRUPTS_ON_CTXSW.
    >>>
    >>> This patch changes the check_context() function to
    >>> check_and_switch_context() called from switch_mm(). In case of
    >>> ASID-capable CPUs (ARMv6 onwards), if a new ASID is needed, it defers
    >>> the __new_context() and cpu_switch_mm() calls to the post-lock switch
    >>> hook where the interrupts are enabled. Setting the reserved TTBR0 was
    >>> also moved to check_and_switch_context() from cpu_v7_switch_mm().
    >>>
    >>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    >>> Cc: Russell King <linux@arm.linux.org.uk>
    >>> ---
    >>> arch/arm/include/asm/mmu_context.h | 81 ++++++++++++++++++++++++++++--------
    >>> arch/arm/include/asm/system.h | 2 +
    >>> arch/arm/include/asm/thread_info.h | 1 +
    >>> arch/arm/mm/context.c | 4 +-
    >>> arch/arm/mm/proc-v7.S | 3 -
    >>> 5 files changed, 69 insertions(+), 22 deletions(-)
    >>>
    >>
    >> < snip >
    >>
    >>> diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
    >>> index 2faff3b..d5334d9 100644
    >>> --- a/arch/arm/mm/proc-v7.S
    >>> +++ b/arch/arm/mm/proc-v7.S
    >>> @@ -116,9 +116,6 @@ ENTRY(cpu_v7_switch_mm)
    >>> #ifdef CONFIG_ARM_ERRATA_430973
    >>> mcr p15, 0, r2, c7, c5, 6 @ flush BTAC/BTB
    >>> #endif
    >>> - mrc p15, 0, r2, c2, c0, 1 @ load TTB 1
    >>> - mcr p15, 0, r2, c2, c0, 0 @ into TTB 0
    >>> - isb
    >>> #ifdef CONFIG_ARM_ERRATA_754322
    >>> dsb
    >>> #endif
    >>
    >> I do not have a tree that matches this version of cpu_v7_switch_mm().
    >> Can you point me at a tree that I can see this in?
    >
    > That's added by the second patch in the series (and removed in a later
    > patch but it is a logical change in both situations and keeps the code
    > bisectable).
    >

    Ah, yes! Thanks.

    -Frank



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