File 5c87e6d1-x86-TSX-controls-for-RTM-force-abort-m... of Package xen

Overview Repositories Revisions Requests Users Attributes Meta

File 5c87e6d1-x86-TSX-controls-for-RTM-force-abort-mode.patch of Package xen (Revision e9eacf6a47ee4eab968005ab9c5f63ce)

Currently displaying revision e9eacf6a47ee4eab968005ab9c5f63ce , Show latest

# Commit 6be613f29b4205349275d24367bd4c82fb2960dd
# Date 2019-03-12 17:05:21 +0000
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/tsx: Implement controls for RTM force-abort mode

The CPUID bit and MSR are deliberately not exposed to guests, because they
won't exist on newer processors.  As vPMU isn't security supported, the
misbehaviour of PCR3 isn't expected to impact production deployments.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -2109,7 +2109,7 @@ Use Virtual Processor ID support if avai
 flushes on VM entry and exit, increasing performance.
 
 ### vpmu (x86)
-    = List of [ <bool>, bts, ipc, arch ]
+    = List of [ <bool>, bts, ipc, arch, rtm-abort=<bool> ]
 
     Applicability: x86.  Default: false
 
@@ -2142,6 +2142,21 @@ provide access to a wealth of low level
 
 *   The `arch` option allows access to the pre-defined architectural events.
 
+*   The `rtm-abort` boolean controls a trade-off between working Restricted
+    Transactional Memory, and working performance counters.
+
+    All processors released to date (Q1 2019) supporting Transactional Memory
+    Extensions suffer an erratum which has been addressed in microcode.
+
+    Processors based on the Skylake microarchitecture with up-to-date
+    microcode internally use performance counter 3 to work around the erratum.
+    A consequence is that the counter gets reprogrammed whenever an `XBEGIN`
+    instruction is executed.
+
+    An alternative mode exists where PCR3 behaves as before, at the cost of
+    `XBEGIN` unconditionally aborting.  Enabling `rtm-abort` mode will
+    activate this alternative mode.
+
 *Warning:*
 As the virtualisation is not 100% safe, don't use the vpmu flag on
 production systems (see http://xenbits.xen.org/xsa/advisory-163.html)!
--- a/tools/misc/xen-cpuid.c
+++ b/tools/misc/xen-cpuid.c
@@ -146,6 +146,8 @@ static const char *str_7d0[32] =
 {
     [ 2] = "avx512_4vnniw", [ 3] = "avx512_4fmaps",
 
+    /* 12 */                [13] = "tsx-force-abort",
+
     [26] = "ibrsb",         [27] = "stibp",
     [28] = "l1d_flush",     [29] = "arch_caps",
     /* 30 */                [31] = "ssbd",
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -286,6 +286,9 @@ static void Intel_errata_workarounds(str
 	if (c->x86 == 6 && cpu_has_clflush &&
 	    (c->x86_model == 29 || c->x86_model == 46 || c->x86_model == 47))
 		__set_bit(X86_FEATURE_CLFLUSH_MONITOR, c->x86_capability);
+
+	if (cpu_has_tsx_force_abort && opt_rtm_abort)
+		wrmsrl(MSR_TSX_FORCE_ABORT, TSX_FORCE_ABORT_RTM);
 }
 
 
--- a/xen/arch/x86/cpu/vpmu.c
+++ b/xen/arch/x86/cpu/vpmu.c
@@ -45,6 +45,7 @@ CHECK_pmu_params;
 static unsigned int __read_mostly opt_vpmu_enabled;
 unsigned int __read_mostly vpmu_mode = XENPMU_MODE_OFF;
 unsigned int __read_mostly vpmu_features = 0;
+bool __read_mostly opt_rtm_abort;
 
 static DEFINE_SPINLOCK(vpmu_lock);
 static unsigned vpmu_count;
@@ -73,6 +74,8 @@ static int __init parse_vpmu_params(cons
             vpmu_features |= XENPMU_FEATURE_IPC_ONLY;
         else if ( !cmdline_strcmp(s, "arch") )
             vpmu_features |= XENPMU_FEATURE_ARCH_ONLY;
+        else if ( (val = parse_boolean("rtm-abort", s, ss)) >= 0 )
+            opt_rtm_abort = val;
         else
             rc = -EINVAL;
 
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -131,6 +131,8 @@ int guest_rdmsr(const struct vcpu *v, ui
     case MSR_PRED_CMD:
     case MSR_FLUSH_CMD:
         /* Write-only */
+    case MSR_TSX_FORCE_ABORT:
+        /* Not offered to guests. */
         goto gp_fault;
 
     case MSR_SPEC_CTRL:
@@ -230,6 +232,8 @@ int guest_wrmsr(struct vcpu *v, uint32_t
     case MSR_INTEL_PLATFORM_INFO:
     case MSR_ARCH_CAPABILITIES:
         /* Read-only */
+    case MSR_TSX_FORCE_ABORT:
+        /* Not offered to guests. */
         goto gp_fault;
 
     case MSR_AMD_PATCHLOADER:
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -112,6 +112,9 @@
 /* CPUID level 0x80000007.edx */
 #define cpu_has_itsc            boot_cpu_has(X86_FEATURE_ITSC)
 
+/* CPUID level 0x00000007:0.edx */
+#define cpu_has_tsx_force_abort boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT)
+
 /* Synthesized. */
 #define cpu_has_arch_perfmon    boot_cpu_has(X86_FEATURE_ARCH_PERFMON)
 #define cpu_has_cpuid_faulting  boot_cpu_has(X86_FEATURE_CPUID_FAULTING)
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -51,6 +51,9 @@
 #define MSR_FLUSH_CMD			0x0000010b
 #define FLUSH_CMD_L1D			(_AC(1, ULL) << 0)
 
+#define MSR_TSX_FORCE_ABORT             0x0000010f
+#define TSX_FORCE_ABORT_RTM             (_AC(1, ULL) <<  0)
+
 /* Intel MSRs. Some also available on other CPUs */
 #define MSR_IA32_PERFCTR0		0x000000c1
 #define MSR_IA32_A_PERFCTR0		0x000004c1
--- a/xen/include/asm-x86/vpmu.h
+++ b/xen/include/asm-x86/vpmu.h
@@ -125,6 +125,7 @@ static inline int vpmu_do_rdmsr(unsigned
 
 extern unsigned int vpmu_mode;
 extern unsigned int vpmu_features;
+extern bool opt_rtm_abort;
 
 /* Context switch */
 static inline void vpmu_switch_from(struct vcpu *prev)
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -242,6 +242,7 @@ XEN_CPUFEATURE(IBPB,          8*32+12) /
 /* Intel-defined CPU features, CPUID level 0x00000007:0.edx, word 9 */
 XEN_CPUFEATURE(AVX512_4VNNIW, 9*32+ 2) /*A  AVX512 Neural Network Instructions */
 XEN_CPUFEATURE(AVX512_4FMAPS, 9*32+ 3) /*A  AVX512 Multiply Accumulation Single Precision */
+XEN_CPUFEATURE(TSX_FORCE_ABORT, 9*32+13) /* MSR_TSX_FORCE_ABORT.RTM_ABORT */
 XEN_CPUFEATURE(IBRSB,         9*32+26) /*A  IBRS and IBPB support (used by Intel) */
 XEN_CPUFEATURE(STIBP,         9*32+27) /*A  STIBP */
 XEN_CPUFEATURE(L1D_FLUSH,     9*32+28) /*S  MSR_FLUSH_CMD and L1D flush. */

Places

File 5c87e6d1-x86-TSX-controls-for-RTM-force-abort-mode.patch of Package xen (Revision e9eacf6a47ee4eab968005ab9c5f63ce)

Places