x86/spec-ctrl: Expose IPRED_CTRL to guests

The CPUID feature bit signals the presence of the IPRED_DIS_{U,S} controls in
SPEC_CTRL MSR, first available in Intel AlderLake and Sapphire Rapids CPUs.

Xen already knows how to context switch MSR_SPEC_CTRL properly between guest
and hypervisor context.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
(cherry picked from commit 4dd6760706848de30f7c8b5f83462b9bcb070c91)

diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index f7192c1ddf58aee2c352eb7b968a750cf4acb831..ac0155359831feda52446f348f62d7401d71b8cf 100644 (file)
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -316,8 +316,8 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
 
 /*
  * Caller to confirm that MSR_SPEC_CTRL is available.  Intel and AMD have
- * separate CPUID features for this functionality, but only set will be
- * active.
+ * separate CPUID features for some of this functionality, but only one
+ * vendors-worth will be active on a single host.
  */
 uint64_t msr_spec_ctrl_valid_bits(const struct cpu_policy *cp)
 {
@@ -331,6 +331,8 @@ uint64_t msr_spec_ctrl_valid_bits(const struct cpu_policy *cp)
     return (SPEC_CTRL_IBRS | SPEC_CTRL_STIBP |
             (ssbd       ? SPEC_CTRL_SSBD       : 0) |
             (psfd       ? SPEC_CTRL_PSFD       : 0) |
+            (cp->feat.ipred_ctrl
+             ? (SPEC_CTRL_IPRED_DIS_U | SPEC_CTRL_IPRED_DIS_S) : 0) |
             0);
 }
 

diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h
index bc971f3c6fbfa167f8f3ed0d80bf776fe4cfc8f0..8708b934a0d2e3fa9a1d3fc26890c9ee814664e8 100644 (file)
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -295,7 +295,7 @@ XEN_CPUFEATURE(INTEL_PPIN,         12*32+ 0) /*   Protected Processor Inventory
 
 /* Intel-defined CPU features, CPUID level 0x00000007:2.edx, word 13 */
 XEN_CPUFEATURE(INTEL_PSFD,         13*32+ 0) /*A  MSR_SPEC_CTRL.PSFD */
-XEN_CPUFEATURE(IPRED_CTRL,         13*32+ 1) /*   MSR_SPEC_CTRL.IPRED_DIS_* */
+XEN_CPUFEATURE(IPRED_CTRL,         13*32+ 1) /*A  MSR_SPEC_CTRL.IPRED_DIS_* */
 XEN_CPUFEATURE(RRSBA_CTRL,         13*32+ 2) /*   MSR_SPEC_CTRL.RRSBA_DIS_* */
 XEN_CPUFEATURE(BHI_CTRL,           13*32+ 4) /*   MSR_SPEC_CTRL.BHI_DIS_S */
 XEN_CPUFEATURE(MCDT_NO,            13*32+ 5) /*A  MCDT_NO */

diff --git a/xen/tools/gen-cpuid.py b/xen/tools/gen-cpuid.py
index 636ff44c8b2d453552c2b96c2247cf6c52562553..9d1e47cfcdf5f42dc45c563f251bd0bce1c4c02a 100755 (executable)
--- a/xen/tools/gen-cpuid.py
+++ b/xen/tools/gen-cpuid.py
@@ -318,7 +318,8 @@ def crunch_numbers(state):
         # IBRSB/IBRS, and we pass this MSR directly to guests.  Treating them
         # as dependent features simplifies Xen's logic, and prevents the guest
         # from seeing implausible configurations.
-        IBRSB: [STIBP, SSBD, INTEL_PSFD, EIBRS],
+        IBRSB: [STIBP, SSBD, INTEL_PSFD, EIBRS,
+                IPRED_CTRL],
         IBRS: [AMD_STIBP, AMD_SSBD, PSFD,
                IBRS_ALWAYS, IBRS_FAST, IBRS_SAME_MODE],
         IBPB: [IBPB_RET, SBPB, IBPB_BRTYPE],