linux-kernel - [PATCH v2] efi/unaccepted: touch soft lockup during memory accept

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Message-Id: <20240411004907.649394-1-yu.c.chen@intel.com>
Date: Thu, 11 Apr 2024 08:49:07 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: linux-efi@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Chao Gao <chao.gao@...el.com>,
	linux-kernel@...r.kernel.org,
	Chen Yu <yu.c.chen@...el.com>,
	"Hossain, Md Iqbal" <md.iqbal.hossain@...el.com>
Subject: [PATCH v2] efi/unaccepted: touch soft lockup during memory accept

Commit 50e782a86c98 ("efi/unaccepted: Fix soft lockups caused
by parallel memory acceptance") has released the spinlock so
other CPUs can do memory acceptance in parallel and not
triggers softlockup on other CPUs.

However the softlock up was intermittent shown up if the memory
of the TD guest is large, and the timeout of softlockup is set
to 1 second.

The symptom is:
When the local irq is enabled at the end of accept_memory(),
the softlockup detects that the watchdog on single CPU has
not been fed for a while. That is to say, even other CPUs
will not be blocked by spinlock, the current CPU might be
stunk with local irq disabled for a while, which hurts not
only nmi watchdog but also softlockup.

Chao Gao pointed out that the memory accept could be time
costly and there was similar report before. Thus to avoid
any softlocup detection during this stage, give the
softlockup a flag to skip the timeout check at the end of
accept_memory(), by invoking touch_softlockup_watchdog().

Fixes: 50e782a86c98 ("efi/unaccepted: Fix soft lockups caused by parallel memory acceptance")
Reported-by: "Hossain, Md Iqbal" <md.iqbal.hossain@...el.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
---
v1 -> v2:
	 Refine the commit log and add fixes tag/reviewed-by tag from Kirill.
---
 drivers/firmware/efi/unaccepted_memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c
index 5b439d04079c..50f6503fe49f 100644
--- a/drivers/firmware/efi/unaccepted_memory.c
+++ b/drivers/firmware/efi/unaccepted_memory.c
@@ -4,6 +4,7 @@
 #include <linux/memblock.h>
 #include <linux/spinlock.h>
 #include <linux/crash_dump.h>
+#include <linux/nmi.h>
 #include <asm/unaccepted_memory.h>

 /* Protects unaccepted memory bitmap and accepting_list */
@@ -149,6 +150,9 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
 	}

 	list_del(&range.list);
+
+	touch_softlockup_watchdog();
+
 	spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
 }

-- 
2.25.1