[Xen-changelog] Disable C1 clock ramping on AMD 8th gen CPUs.

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID eb6d2472ea1ac1275b2382735959217d26cc7933
# Parent  34f6a1efe52d8c5c722a2d423a0b26b469540a3a
Disable C1 clock ramping on AMD 8th gen CPUs.

This reverts a previous changeset that removed this code.
It is currently required for good TSC behaviour in SVM
(fully virtualised) guests.

Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>

diff -r 34f6a1efe52d -r eb6d2472ea1a xen/arch/x86/cpu/amd.c
--- a/xen/arch/x86/cpu/amd.c    Fri Feb 17 18:35:38 2006
+++ b/xen/arch/x86/cpu/amd.c    Fri Feb 17 19:41:30 2006
@@ -41,6 +41,62 @@
  
 extern void vide(void);
 __asm__(".text\n.align 4\nvide: ret");
+
+/* Can this system suffer from TSC drift due to C1 clock ramping? */
+static int c1_ramping_may_cause_clock_drift(struct cpuinfo_x86 *c) 
+{ 
+       if (c->x86 < 0xf) {
+               /*
+                * TSC drift doesn't exist on 7th Gen or less
+                * However, OS still needs to consider effects
+                * of P-state changes on TSC
+                */
+               return 0;
+       } else if (cpuid_edx(0x80000007) & (1<<8)) {
+               /*
+                * CPUID.AdvPowerMgmtInfo.TscInvariant
+                * EDX bit 8, 8000_0007
+                * Invariant TSC on 8th Gen or newer, use it
+                * (assume all cores have invariant TSC)
+                */
+               return 0;
+       }
+       return 1;
+}
+
+/* PCI access functions. Should be safe to use 0xcf8/0xcfc port accesses here. 
*/
+static u8 pci_read_byte(u32 bus, u32 dev, u32 fn, u32 reg)
+{
+       outl((1U<<31) | (bus << 16) | (dev << 11) | (fn << 8) | (reg & ~3), 
0xcf8);
+       return inb(0xcfc + (reg & 3));
+}
+
+static void pci_write_byte(u32 bus, u32 dev, u32 fn, u32 reg, u8 val)
+{
+       outl((1U<<31) | (bus << 16) | (dev << 11) | (fn << 8) | (reg & ~3), 
0xcf8);
+       outb(val, 0xcfc + (reg & 3));
+}
+
+/*
+ * Disable C1-Clock ramping if enabled in PMM7.CpuLowPwrEnh on 8th-generation
+ * cores only. Assume BIOS has setup all Northbridges equivalently.
+ */
+static void disable_c1_ramping(void) 
+{
+       u8 pmm7;
+       int node;
+
+       for (node=0; node < NR_CPUS; node++) {
+               /* PMM7: bus=0, dev=0x18+node, function=0x3, register=0x87. */
+               pmm7 = pci_read_byte(0, 0x18+node, 0x3, 0x87);
+               /* Invalid read means we've updated every Northbridge. */
+               if (pmm7 == 0xFF)
+                       break;
+               pmm7 &= 0xFC; /* clear pmm7[1:0] */
+               pci_write_byte(0, 0x18+node, 0x3, 0x87, pmm7);
+               printk ("AMD: Disabling C1 Clock Ramping Node #%x\n", node);
+       }
+}
 
 static void __init init_amd(struct cpuinfo_x86 *c)
 {
@@ -274,6 +330,10 @@
                       cpu, c->x86_max_cores, cpu_core_id[cpu]);
        }
 #endif
+
+       /* Prevent TSC drift in non single-processor, single-core platforms. */
+       if ((smp_processor_id() == 1) && c1_ramping_may_cause_clock_drift(c))
+               disable_c1_ramping();
 
        start_svm();
 }

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