linux-kernel - [PATCH v7 6/6] x86/split_lock: Fix the split lock #AC handling when running as guest

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Date:   Tue,  5 Oct 2021 16:05:50 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v7 6/6] x86/split_lock: Fix the split lock #AC handling when running as guest

From: Xiaoyao Li <xiaoyao.li@...el.com>

If running as guest and hypervisor enables
MSR_TEST_CTRL.SPLIT_LOCK_DETECT during its running, it can get split
lock #AC even though sld_state is sld_off.

For kernel mode #AC, it always dies("split lock"), no more action
needed.

For user mode #AC, it should treat sld_off (default state when feature
is not available) as fatal as well.

Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
---
 arch/x86/kernel/cpu/intel.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 01d7935feaed..47f0bc95ce2a 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1190,7 +1190,12 @@ static void bus_lock_init(void)
 
 bool handle_user_split_lock(struct pt_regs *regs, long error_code)
 {
-	if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
+	/*
+	 * In virtualization environment, it can get split lock #AC even when
+	 * sld_off but hypervisor enables it.
+	 * Thus only handles when sld_warn explicitly.
+	 */
+	if ((regs->flags & X86_EFLAGS_AC) || sld_state != sld_warn)
 		return false;
 	split_lock_warn(regs->ip);
 	return true;
-- 
2.25.1