linux-kernel - [PATCHv3] iommu/intel: Ratelimit each dmar fault printing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20180215191729.15777-1-dima@arista.com>
Date:   Thu, 15 Feb 2018 19:17:29 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     0x7f454c46@...il.com, Dmitry Safonov <dima@...sta.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org
Subject: [PATCHv3] iommu/intel: Ratelimit each dmar fault printing

There is a ratelimit for printing, but it's incremented each time the
cpu recives dmar fault interrupt. While one interrupt may signal about
*many* faults.
So, measuring the impact it turns out that reading/clearing one fault
takes < 1 usec, and printing info about the fault takes ~170 msec.

Having in mind that maximum number of fault recording registers per
remapping hardware unit is 256.. IRQ handler may run for (170*256) msec.
And as fault-serving loop runs without a time limit, during servicing
new faults may occur..

Ratelimit each fault printing rather than each irq printing.

Fixes: commit c43fce4eebae ("iommu/vt-d: Ratelimit fault handler")

BUG: spinlock lockup suspected on CPU#0, CliShell/9903
 lock: 0xffffffff81a47440, .magic: dead4ead, .owner: kworker/u16:2/8915, .owner_cpu: 6
CPU: 0 PID: 9903 Comm: CliShell
Call Trace:$\n'
[..] dump_stack+0x65/0x83$\n'
[..] spin_dump+0x8f/0x94$\n'
[..] do_raw_spin_lock+0x123/0x170$\n'
[..] _raw_spin_lock_irqsave+0x32/0x3a$\n'
[..] uart_chars_in_buffer+0x20/0x4d$\n'
[..] tty_chars_in_buffer+0x18/0x1d$\n'
[..] n_tty_poll+0x1cb/0x1f2$\n'
[..] tty_poll+0x5e/0x76$\n'
[..] do_select+0x363/0x629$\n'
[..] compat_core_sys_select+0x19e/0x239$\n'
[..] compat_SyS_select+0x98/0xc0$\n'
[..] sysenter_dispatch+0x7/0x25$\n'
[..]
NMI backtrace for cpu 6
CPU: 6 PID: 8915 Comm: kworker/u16:2
Workqueue: dmar_fault dmar_fault_work
Call Trace:$\n'
[..] wait_for_xmitr+0x26/0x8f$\n'
[..] serial8250_console_putchar+0x1c/0x2c$\n'
[..] uart_console_write+0x40/0x4b$\n'
[..] serial8250_console_write+0xe6/0x13f$\n'
[..] call_console_drivers.constprop.13+0xce/0x103$\n'
[..] console_unlock+0x1f8/0x39b$\n'
[..] vprintk_emit+0x39e/0x3e6$\n'
[..] printk+0x4d/0x4f$\n'
[..] dmar_fault+0x1a8/0x1fc$\n'
[..] dmar_fault_work+0x15/0x17$\n'
[..] process_one_work+0x1e8/0x3a9$\n'
[..] worker_thread+0x25d/0x345$\n'
[..] kthread+0xea/0xf2$\n'
[..] ret_from_fork+0x58/0x90$\n'

Cc: Alex Williamson <alex.williamson@...hat.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Joerg Roedel <joro@...tes.org>
Cc: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: iommu@...ts.linux-foundation.org
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
Maybe it's worth to limit while(1) cycle.
If IOMMU generates faults with equal speed as irq handler cleans
them, it may turn into long-irq-disabled region again.
Not sure if it can happen anyway.

 drivers/iommu/dmar.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index accf58388bdb..6c4ea32ee6a9 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -1618,17 +1618,13 @@ irqreturn_t dmar_fault(int irq, void *dev_id)
 	int reg, fault_index;
 	u32 fault_status;
 	unsigned long flag;
-	bool ratelimited;
 	static DEFINE_RATELIMIT_STATE(rs,
 				      DEFAULT_RATELIMIT_INTERVAL,
 				      DEFAULT_RATELIMIT_BURST);
 
-	/* Disable printing, simply clear the fault when ratelimited */
-	ratelimited = !__ratelimit(&rs);
-
 	raw_spin_lock_irqsave(&iommu->register_lock, flag);
 	fault_status = readl(iommu->reg + DMAR_FSTS_REG);
-	if (fault_status && !ratelimited)
+	if (fault_status && __ratelimit(&rs))
 		pr_err("DRHD: handling fault status reg %x\n", fault_status);
 
 	/* TBD: ignore advanced fault log currently */
@@ -1638,6 +1634,8 @@ irqreturn_t dmar_fault(int irq, void *dev_id)
 	fault_index = dma_fsts_fault_record_index(fault_status);
 	reg = cap_fault_reg_offset(iommu->cap);
 	while (1) {
+		/* Disable printing, simply clear the fault when ratelimited */
+		bool ratelimited = !__ratelimit(&rs);
 		u8 fault_reason;
 		u16 source_id;
 		u64 guest_addr;
-- 
2.13.6