From: Matthew Dillon <dillon@apollo.backplane.com>
Date: Fri, 24 Aug 2012 03:41:26 +0000 (-0700)
Subject: kernel - Implement Errata 721 for 32-bit kernels too
X-Git-Tag: v3.2.0~273
X-Git-Url: https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff_plain/e917a7645571ee28f67a9bd1c358dbcda9161d18

kernel - Implement Errata 721 for 32-bit kernels too

* The AMD errata 721 definitely happens on cpus running in cpu bit mode
  but I got a weird kernel crash on 32-bit (which I don't have time to
  follow up) so I decided, what the heck, might as well do it on 32-bit
  boxes too.
---

diff --git a/sys/platform/pc32/i386/initcpu.c b/sys/platform/pc32/i386/initcpu.c
index 4854d43490..6407f4eda9 100644
--- a/sys/platform/pc32/i386/initcpu.c
+++ b/sys/platform/pc32/i386/initcpu.c
@@ -636,6 +636,8 @@ init_686_amd(void)
 void
 initializecpu(void)
 {
+	uint64_t msr;
+
 	switch (cpu) {
 #ifdef I486_CPU
 	case CPU_BLUE:
@@ -697,6 +699,28 @@ initializecpu(void)
 	}
 	enable_sse();
 
+	if (cpu_vendor_id == CPU_VENDOR_AMD) {
+		switch((cpu_id & 0xFF0000)) {
+		case 0x100000:
+		case 0x120000:
+			/*
+			 * Errata 721 is the cpu bug found by your's truly
+			 * (Matthew Dillon).  It is a bug where a sequence
+			 * of 5 or more popq's + a retq, under involved
+			 * deep recursion circumstances, can cause the %rsp
+			 * to not be properly updated, almost always
+			 * resulting in a seg-fault soon after.
+			 */
+			msr = rdmsr(0xc0011029);
+			if ((msr & 1) == 0) {
+				kprintf("Errata 721 workaround installed\n");
+				msr |= 1;
+				wrmsr(0xc0011029, msr);
+			}
+			break;
+		}
+	}
+
 	if (cpu_feature2 & CPUID2_VMM)
 		vmm_guest = 1;