x86/spec-ctrl: CPUID/MSR definitions for L1D_FLUSH

This is part of XSA-273 / CVE-2018-3646.

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

--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -442,10 +442,10 @@ accounting for hardware capabilities as
 
 Currently accepted:
 
-The Speculation Control hardware features `ibrsb`, `stibp`, `ibpb`, `ssbd` are
-used by default if available and applicable.  They can be ignored,
-e.g. `no-ibrsb`, at which point Xen won't use them itself, and won't offer
-them to guests.
+The Speculation Control hardware features `ibrsb`, `stibp`, `ibpb`,
+`l1d-flush` and `ssbd` are used by default if available and applicable.  They can
+be ignored, e.g. `no-ibrsb`, at which point Xen won't use them itself, and
+won't offer them to guests.
 
 ### cpuid\_mask\_cpu (AMD only)
 > `= fam_0f_rev_c | fam_0f_rev_d | fam_0f_rev_e | fam_0f_rev_f | fam_0f_rev_g | fam_10_rev_b | fam_10_rev_c | fam_11_rev_b`
--- a/tools/libxl/libxl_cpuid.c
+++ b/tools/libxl/libxl_cpuid.c
@@ -160,6 +160,7 @@ int libxl_cpuid_parse_config(libxl_cpuid
         {"fpu",          0x00000001, NA, CPUID_REG_EDX,  0,  1},
         {"ibrsb",        0x00000007,  0, CPUID_REG_EDX, 26,  1},
         {"stibp",        0x00000007,  0, CPUID_REG_EDX, 27,  1},
+        {"l1d-flush",    0x00000007,  0, CPUID_REG_EDX, 28,  1},
         {"arch-caps",    0x00000007,  0, CPUID_REG_EDX, 29,  1},
         {"ssbd",         0x00000007,  0, CPUID_REG_EDX, 31,  1},
         {"topoext",      0x80000001, NA, CPUID_REG_ECX, 22,  1},
--- a/tools/misc/xen-cpuid.c
+++ b/tools/misc/xen-cpuid.c
@@ -152,7 +152,7 @@ static const char *str_7d0[32] =
     [0 ... 25] = "REZ",
 
     [26] = "ibrsb",         [27] = "stibp",
-    [28] = "REZ",           [29] = "arch_caps",
+    [28] = "l1d_flush",     [29] = "arch_caps",
     [30] = "REZ",           [31] = "ssbd",
 };
 
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -42,6 +42,11 @@ static int __init parse_xen_cpuid(const
             if ( !val )
                 setup_clear_cpu_cap(X86_FEATURE_STIBP);
         }
+        else if ( (val = parse_boolean("l1d-flush", s, ss)) >= 0 )
+        {
+            if ( !val )
+                setup_clear_cpu_cap(X86_FEATURE_L1D_FLUSH);
+        }
         else if ( (val = parse_boolean("ssbd", s, ss)) >= 0 )
         {
             if ( !val )
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -249,14 +249,16 @@ static void __init print_details(enum in
     printk("Speculative mitigation facilities:\n");
 
     /* Hardware features which pertain to speculative mitigations. */
-    printk("  Hardware features:%s%s%s%s%s%s%s%s\n",
+    printk("  Hardware features:%s%s%s%s%s%s%s%s%s%s\n",
            (_7d0 & cpufeat_mask(X86_FEATURE_IBRSB)) ? " IBRS/IBPB" : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_STIBP)) ? " STIBP"     : "",
+           (_7d0 & cpufeat_mask(X86_FEATURE_L1D_FLUSH)) ? " L1D_FLUSH" : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_SSBD))  ? " SSBD"      : "",
            (e8b  & cpufeat_mask(X86_FEATURE_IBPB))  ? " IBPB"      : "",
            (caps & ARCH_CAPABILITIES_IBRS_ALL)      ? " IBRS_ALL"  : "",
            (caps & ARCH_CAPABILITIES_RDCL_NO)       ? " RDCL_NO"   : "",
            (caps & ARCH_CAPS_RSBA)                  ? " RSBA"      : "",
+           (caps & ARCH_CAPS_SKIP_L1DFL)            ? " SKIP_L1DFL": "",
            (caps & ARCH_CAPS_SSB_NO)                ? " SSB_NO"    : "");
 
     /* Compiled-in support which pertains to mitigations. */
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -44,8 +44,12 @@
 #define ARCH_CAPABILITIES_RDCL_NO	(_AC(1, ULL) << 0)
 #define ARCH_CAPABILITIES_IBRS_ALL	(_AC(1, ULL) << 1)
 #define ARCH_CAPS_RSBA			(_AC(1, ULL) << 2)
+#define ARCH_CAPS_SKIP_L1DFL		(_AC(1, ULL) << 3)
 #define ARCH_CAPS_SSB_NO		(_AC(1, ULL) << 4)
 
+#define MSR_FLUSH_CMD			0x0000010b
+#define FLUSH_CMD_L1D			(_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/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -229,6 +229,7 @@ XEN_CPUFEATURE(IBPB,          8*32+12) /
 /* Intel-defined CPU features, CPUID level 0x00000007:0.edx, word 9 */
 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) /*   MSR_FLUSH_CMD and L1D flush. */
 XEN_CPUFEATURE(ARCH_CAPS,     9*32+29) /*   IA32_ARCH_CAPABILITIES MSR */
 XEN_CPUFEATURE(SSBD,          9*32+31) /*A  MSR_SPEC_CTRL.SSBD available */
 
