linux-kernel - [PATCH 2/3] x86/bus_lock: Add support for AMD

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Date: Mon, 29 Apr 2024 11:36:42 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<thomas.lendacky@....com>
CC: <ravi.bangoria@....com>, <hpa@...or.com>, <rmk+kernel@...linux.org.uk>,
	<peterz@...radead.org>, <james.morse@....com>, <lukas.bulwahn@...il.com>,
	<arjan@...ux.intel.com>, <j.granados@...sung.com>, <sibs@...natelecom.cn>,
	<nik.borisov@...e.com>, <michael.roth@....com>, <nikunj.dadhania@....com>,
	<babu.moger@....com>, <x86@...nel.org>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <santosh.shukla@....com>,
	<ananth.narayan@....com>, <sandipan.das@....com>
Subject: [PATCH 2/3] x86/bus_lock: Add support for AMD

Upcoming AMD uarch will support Bus Lock Detect (called Bus Lock Trap
in AMD docs). Add support for the same in Linux. Bus Lock Detect is
enumerated with cpuid CPUID Fn0000_0007_ECX_x0 bit [24 / BUSLOCKTRAP].
It can be enabled through MSR_IA32_DEBUGCTLMSR. When enabled, hardware
clears DR6[11] and raises a #DB exception on occurrence of Bus Lock if
CPL > 0. More detail about the feature can be found in AMD APM[1].

[1]: AMD64 Architecture Programmer's Manual Pub. 40332, Rev. 4.07 - June
     2023, Vol 2, 13.1.3.6 Bus Lock Trap
     https://bugzilla.kernel.org/attachment.cgi?id=304653

Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
---
 arch/x86/kernel/cpu/amd.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 39f316d50ae4..013d16479a24 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1058,6 +1058,8 @@ static void init_amd(struct cpuinfo_x86 *c)
 
 	/* AMD CPUs don't need fencing after x2APIC/TSC_DEADLINE MSR writes. */
 	clear_cpu_cap(c, X86_FEATURE_APIC_MSRS_FENCE);
+
+	bus_lock_init();
 }
 
 #ifdef CONFIG_X86_32
-- 
2.44.0