[PATCH] x86/S3: Restore CR4 earlier during resume

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s 4304ff420e5 "x86/S3: Drop {save,restore}_rest_processor_state()
completely" moved CR4 restoration up into C, to account for the fact that MCE
was explicitly handled later.

However, time_resume() ends up making an EFI Runtime Service call, and EFI
explodes without OSFXSR, presumably when trying to spill %xmm registers onto
the stack.

Given this codepath, and the potential for other issues of a similar kind (TLB
flushing vs INVPCID, HVM logic vs VMXE, etc), restore CR4 in asm before
entering C.

Ignore the previous MCE special case, because its not actually necessary.  The
handler is already suitably configured from before suspend.

Fixes: 4304ff420e5 ("x86/S3: Drop {save,restore}_rest_processor_state() 
completely")
Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

This is one definite bug fix.  It doesn't appear to be the only S3 bug
however.
---
 xen/arch/x86/acpi/power.c       | 3 ---
 xen/arch/x86/acpi/wakeup_prot.S | 5 +++++
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
index 4fb1e7a148..7f162a4df9 100644
--- a/xen/arch/x86/acpi/power.c
+++ b/xen/arch/x86/acpi/power.c
@@ -276,9 +276,6 @@ static int enter_state(u32 state)
 
     mcheck_init(&boot_cpu_data, false);
 
-    /* Restore CR4 from cached value, now MCE is set up. */
-    write_cr4(read_cr4());
-
     printk(XENLOG_INFO "Finishing wakeup from ACPI S%d state.\n", state);
 
     if ( (state == ACPI_STATE_S3) && error )
diff --git a/xen/arch/x86/acpi/wakeup_prot.S b/xen/arch/x86/acpi/wakeup_prot.S
index c6b3fcc93d..1ee5551fb5 100644
--- a/xen/arch/x86/acpi/wakeup_prot.S
+++ b/xen/arch/x86/acpi/wakeup_prot.S
@@ -110,6 +110,11 @@ ENTRY(s3_resume)
 
         call    load_system_tables
 
+        /* Restore CR4 from the cpuinfo block. */
+        GET_STACK_END(bx)
+        mov     STACK_CPUINFO_FIELD(cr4)(%rbx), %rax
+        mov     %rax, %cr4
+
 .Lsuspend_err:
         pop     %r15
         pop     %r14
-- 
2.11.0