[xen stable-4.18] x86/spec-ctrl: Expose IPRED_CTRL to guests

[patchbot@xxxxxxx]

commit fa7f2f9a8618f849380d203c7f18cc8ab12df5fa
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Jan 30 10:13:58 2024 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Apr 9 16:45:01 2024 +0100

    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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    (cherry picked from commit 4dd6760706848de30f7c8b5f83462b9bcb070c91)
---
 xen/arch/x86/msr.c                          | 6 ++++--
 xen/include/public/arch-x86/cpufeatureset.h | 2 +-
 xen/tools/gen-cpuid.py                      | 3 ++-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index c33dc78cd8..54d3752e93 100644
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -309,8 +309,8 @@ 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)
 {
@@ -324,6 +324,8 @@ 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 f3f745ef61..8b7e7d29eb 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -300,7 +300,7 @@ 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(DDP_CTRL,           13*32+ 3) /*   MSR_SPEC_CTRL.DDP_DIS_U */
 XEN_CPUFEATURE(BHI_CTRL,           13*32+ 4) /*   MSR_SPEC_CTRL.BHI_DIS_S */
diff --git a/xen/tools/gen-cpuid.py b/xen/tools/gen-cpuid.py
index 9aa59ffdb1..18f0693d33 100755
--- 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, AUTO_IBRS,
                IBRS_ALWAYS, IBRS_FAST, IBRS_SAME_MODE],
         IBPB: [IBPB_RET, SBPB, IBPB_BRTYPE],
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18