git: 8eebd9592e3d - stable/13 - mca: Handle inconsistent CMCI capability reporting

[Mark Johnston]

The branch stable/13 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=8eebd9592e3daf80c2c743666614119d6c862186

commit 8eebd9592e3daf80c2c743666614119d6c862186
Author:     Mark Johnston <markj at FreeBSD.org>
AuthorDate: 2021-02-08 19:42:54 +0000
Commit:     Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-02-15 19:12:41 +0000

    mca: Handle inconsistent CMCI capability reporting
    
    A BIOS bug may apparently cause the BSP to report that it does not
    implement CMCI, with some APs reporting that they do.  In this scenario,
    avoid a NULL pointer dereference that occurs in cmci_monitor() because
    cmc_state was not allocated by the BSP.
    
    PR:             253272
    Reported by:    asomers, mmacy
    Reviewed by:    kib (previous version)
    
    (cherry picked from commit b5770470276268acef21368b3e77a325df883500)
---
 sys/x86/x86/mca.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/sys/x86/x86/mca.c b/sys/x86/x86/mca.c
index 03100e77d455..801e18073a52 100644
--- a/sys/x86/x86/mca.c
+++ b/sys/x86/x86/mca.c
@@ -1070,6 +1070,20 @@ cmci_monitor(int i)
 
 	KASSERT(i < mca_banks, ("CPU %d has more MC banks", PCPU_GET(cpuid)));
 
+	/*
+	 * It is possible for some APs to report CMCI support even if the BSP
+	 * does not, apparently due to a BIOS bug.
+	 */
+	if (cmc_state == NULL) {
+		if (bootverbose) {
+			printf(
+		    "AP %d (%d,%d) reports CMCI support but the BSP does not\n",
+			    PCPU_GET(cpuid), PCPU_GET(apic_id),
+			    PCPU_GET(acpi_id));
+		}
+		return;
+	}
+
 	ctl = rdmsr(MSR_MC_CTL2(i));
 	if (ctl & MC_CTL2_CMCI_EN)
 		/* Already monitored by another CPU. */
@@ -1114,6 +1128,10 @@ cmci_resume(int i)
 
 	KASSERT(i < mca_banks, ("CPU %d has more MC banks", PCPU_GET(cpuid)));
 
+	/* See cmci_monitor(). */
+	if (cmc_state == NULL)
+		return;
+
 	/* Ignore banks not monitored by this CPU. */
 	if (!(PCPU_GET(cmci_mask) & 1 << i))
 		return;