linux-kernel - [PATCH V7 06/18] x86/fault: Adjust WARN

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Date:   Tue,  3 Aug 2021 21:32:19 -0700
From:   ira.weiny@...el.com
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev,
        linux-mm@...ck.org
Subject: [PATCH V7 06/18] x86/fault: Adjust WARN_ON for PKey fault

From: Ira Weiny <ira.weiny@...el.com>

Previously if a Protection key fault occurred it indicated something
very wrong because user page mappings are not supposed to be in the
kernel address space.

Now PKey faults may happen on kernel mappings if the feature is enabled.

Remove the warning in the fault path and allow the oops to occur without
extra debugging if PKS is enabled.

Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Ira Weiny <ira.weiny@...el.com>
---
 arch/x86/mm/fault.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index b2eefdefc108..e133c0ed72a0 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1141,11 +1141,15 @@ do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
 		   unsigned long address)
 {
 	/*
-	 * Protection keys exceptions only happen on user pages.  We
-	 * have no user pages in the kernel portion of the address
-	 * space, so do not expect them here.
+	 * X86_PF_PK (Protection key exceptions) may occur on kernel addresses
+	 * when PKS (PKeys Supervisor) is enabled.
+	 *
+	 * However, if PKS is not enabled WARN if this exception is seen
+	 * because there are no user pages in the kernel portion of the address
+	 * space.
 	 */
-	WARN_ON_ONCE(hw_error_code & X86_PF_PK);
+	WARN_ON_ONCE(!cpu_feature_enabled(X86_FEATURE_PKS) &&
+		     (hw_error_code & X86_PF_PK));
 
 #ifdef CONFIG_X86_32
 	/*
-- 
2.28.0.rc0.12.gb6a658bd00c9