linux-kernel - [PATCH v2] x86/platform/uv: Dont use smp_processor

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Message-Id: <20220922200035.94823-1-mike.travis@hpe.com>
Date:   Thu, 22 Sep 2022 15:00:35 -0500
From:   Mike Travis <mike.travis@....com>
To:     Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steve Wahl <steve.wahl@....com>, x86@...nel.org
Cc:     Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        stable@...r.kernel.org, Andy Shevchenko <andy@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: [PATCH v2] x86/platform/uv: Dont use smp_processor_id while preemptible

To avoid a "BUG: using smp_processor_id() in preemptible" debug warning
message, disable preemption around use of the processor id.  This code
sequence merely decides which portal that this CPU uses to read the RTC.
It does this to avoid thrashing the cache but even if preempted it still
reads the same time from the single RTC clock.

Signed-off-by: Mike Travis <mike.travis@....com>
Reviewed-by: Steve Wahl <steve.wahl@....com>
Reviewed-by: Dimitri Sivanich <dimitri.sivanich@....com>
Cc: stable@...r.kernel.org
---
v2: modify patch description, add Cc:stable tag
---
 arch/x86/platform/uv/uv_time.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/platform/uv/uv_time.c b/arch/x86/platform/uv/uv_time.c
index 54663f3e00cb..094190814a28 100644
--- a/arch/x86/platform/uv/uv_time.c
+++ b/arch/x86/platform/uv/uv_time.c
@@ -275,14 +275,17 @@ static int uv_rtc_unset_timer(int cpu, int force)
  */
 static u64 uv_read_rtc(struct clocksource *cs)
 {
-	unsigned long offset;
+	unsigned long offset, time;
+	unsigned int cpu = get_cpu();
 
 	if (uv_get_min_hub_revision_id() == 1)
 		offset = 0;
 	else
-		offset = (uv_blade_processor_id() * L1_CACHE_BYTES) % PAGE_SIZE;
+		offset = (uv_cpu_blade_processor_id(cpu) * L1_CACHE_BYTES) % PAGE_SIZE;
 
-	return (u64)uv_read_local_mmr(UVH_RTC | offset);
+	time = (u64)uv_read_local_mmr(UVH_RTC | offset);
+	put_cpu();
+	return time;
 }
 
 /*
-- 
2.26.2