[xen stable-4.15] x86/spec-ctrl: Don't use spec_ctrl_{enter,exit}_idle() for S3

[patchbot@xxxxxxx]

commit 21dd4ef9a6a59655cfa06550e331557e197324fa
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Jan 28 12:03:42 2022 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Feb 4 16:26:50 2022 +0000

    x86/spec-ctrl: Don't use spec_ctrl_{enter,exit}_idle() for S3
    
    'idle' here refers to hlt/mwait.  The S3 path isn't an idle path - it is a
    platform reset.
    
    We need to load default_xen_spec_ctrl unilaterally on the way back up.
    Currently it happens as a side effect of X86_FEATURE_SC_MSR_IDLE or the next
    return-to-guest, but that's fragile behaviour.
    
    Conversely, there is no need to clear IBRS and flush the store buffers on 
the
    way down; we're microseconds away from cutting power.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 71fac402e05ade7b0af2c34f77517449f6f7e2c1)
---
 xen/arch/x86/acpi/power.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
index 31a56f02d0..0837a3ead4 100644
--- a/xen/arch/x86/acpi/power.c
+++ b/xen/arch/x86/acpi/power.c
@@ -248,7 +248,6 @@ static int enter_state(u32 state)
         error = 0;
 
     ci = get_cpu_info();
-    spec_ctrl_enter_idle(ci);
     /* Avoid NMI/#MC using MSR_SPEC_CTRL until we've reloaded microcode. */
     ci->spec_ctrl_flags &= ~SCF_ist_wrmsr;
 
@@ -295,7 +294,9 @@ static int enter_state(u32 state)
 
     /* Re-enabled default NMI/#MC use of MSR_SPEC_CTRL. */
     ci->spec_ctrl_flags |= (default_spec_ctrl_flags & SCF_ist_wrmsr);
-    spec_ctrl_exit_idle(ci);
+
+    if ( boot_cpu_has(X86_FEATURE_IBRSB) )
+        wrmsrl(MSR_SPEC_CTRL, default_xen_spec_ctrl);
 
     if ( boot_cpu_has(X86_FEATURE_SRBDS_CTRL) )
         wrmsrl(MSR_MCU_OPT_CTRL, default_xen_mcu_opt_ctrl);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.15