lkml.org 
[lkml]   [2017]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] Prevent timer value 0 for MWAITX
From
Date
On 4/25/2017 4:44 PM, Janakarajan Natarajan wrote:
> This patch prevents the value 0 from being used for the MWAITX timer.
>
> Newer hardware has uncovered a bug in the software implementation of
> using MWAITX for the delay function. A value of 0 for the timer is meant
> to indicate that a timeout will not be used to exit MWAITX. On newer
> hardware this can result in MWAITX never returning, resulting in NMI
> soft lockup messages being printed. On older hardware, some of the other
> conditions under which MWAITX can exit masked this issue. The AMD APM
> does not currently document this and will be updated.
>
> Please refer to http://marc.info/?l=kvm&m=148950623231140 for
> information regarding NMI soft lockup messages on an AMD Ryzen 1800X.
> This has been root-caused as a 0 passed to MWAITX causing it to wait
> indefinitely.
>
> This change has the added benefit of avoiding the unnecessary setup of
> MONITORX/MWAITX when the delay value is zero.
>
> Cc: <stable@vger.kernel.org> # 4.4.x+
>
> Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
I know it's late in the cycle, but is there a possibility that this will
make it into 4.11? It is a trivial fix and this issue is seen by folks
outside.
> ---
> arch/x86/lib/delay.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
> index a8e91ae..29df077 100644
> --- a/arch/x86/lib/delay.c
> +++ b/arch/x86/lib/delay.c
> @@ -93,6 +93,13 @@ static void delay_mwaitx(unsigned long __loops)
> {
> u64 start, end, delay, loops = __loops;
>
> + /*
> + * Timer value of 0 causes MWAITX to wait indefinitely, unless there
> + * is a store on the memory monitored by MONITORX.
> + */
> + if (loops == 0)
> + return;
> +
> start = rdtsc_ordered();
>
> for (;;) {

\
 
 \ /
  Last update: 2017-04-27 19:07    [W:0.097 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site