lkml.org 
[lkml]   [2017]   [Dec]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch 3/3] x86/mm: Remove preempt_disable/enable() from __native_flush_tlb()

The cleanup looks good to me, just a few speling nits:

* Thomas Gleixner <tglx@linutronix.de> wrote:

> The preempt_disable/enable() pair in __native_flush_tlb() was added in
> commit 5cf0791da5c1 ("x86/mm: Disable preemption during CR3 read+write") to
> protect the UP variant of flush_tlb_mm_range().
>
> That preempt_disable/enable() pair should have been added to the UP variant
> of flush_tlb_mm_range() instead.
>
> The UP variant was removed with commit ce4a4e565f52 ("x86/mm: Remove the UP
> asm/tlbflush.h code, always use the (formerly) SMP code"), but the
> preempt_disable/enable() pair stayed around.
>
> The latest change to __native_flush_tlb() in commit 6fd166aae78c ("x86/mm:
> Use/Fix PCID to optimize user/kernel switches") added an access to a per
> cpu variable outside the preempt disabled regions which makes no sense at
> all. __native_flush_tlb() must always be called with at least preemption
> disabled.

s/cpu/CPU

>
> Remove the preempt_disable/enable() pair and add a WARN_ON_ONCE() to catch
> bad callers independent of the smp_processor_id() debugging.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/include/asm/tlbflush.h | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -345,15 +345,17 @@ static inline void invalidate_user_asid(
> */
> static inline void __native_flush_tlb(void)
> {
> - invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid));
> /*
> - * If current->mm == NULL then we borrow a mm which may change
> - * during a task switch and therefore we must not be preempted
> - * while we write CR3 back:
> + * Preemption or interrupts must be disabled to protect the access
> + * to the per cpu variable and to prevent being preempted between
> + * read_cr3() and write_cr3().
> */
> - preempt_disable();
> + WARN_ON_ONCE(preemptible());
> +
> + invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid));
> +
> + /* If current->mm == NULL then the read_cr3() "borrows" a mm */
> native_write_cr3(__native_read_cr3());
> - preempt_enable();

s/a mm/an mm

Reviewed-by: Ingo Molnar <mingo@kernel.org>

Thanks,

Ingo

\
 
 \ /
  Last update: 2017-12-30 22:32    [W:0.082 / U:0.680 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site