[Xen-devel] [PATCH] xen/x86: Be more power-efficient when waiting forever

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The effect is unchanged, but the processor will be spending most of its time
in the C1 or C1E power state rather than C0.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

---

This was discovered while I was playing about in the early_page_fault()
handler with the IBM box which was corruption the Xen code section.

There is one final for(;;); loop, but is in common code and immediately
following a call to panic(), so is actually dead code and will be cleaned up
in v2 of my "noreturn" series at the start of 4.5

George: I am requesting that this get a freeze exception, under the
qualification of #2 "An awesome release", given no function change threatening
---
 xen/arch/x86/efi/boot.c |    3 ++-
 xen/arch/x86/traps.c    |    3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/efi/boot.c b/xen/arch/x86/efi/boot.c
index 0dd935c..602cc12 100644
--- a/xen/arch/x86/efi/boot.c
+++ b/xen/arch/x86/efi/boot.c
@@ -201,7 +201,8 @@ static void __init __attribute__((__noreturn__)) 
blexit(const CHAR16 *str)
         efi_bs->FreePages(xsm.addr, PFN_UP(xsm.size));
 
     efi_bs->Exit(efi_ih, EFI_SUCCESS, 0, NULL);
-    for( ; ; ); /* not reached */
+    for ( ; ; ) /* not reached */
+        halt();
 }
 
 /* generic routine for printing error messages */
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index d8b3eac..8c355e5 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1448,7 +1448,8 @@ void __init do_early_page_fault(struct cpu_user_regs 
*regs)
         printk("Stack dump: ");
         while ( ((long)stk & ((PAGE_SIZE - 1) & ~(BYTES_PER_LONG - 1))) != 0 )
             printk("%p ", _p(*stk++));
-        for ( ; ; ) ;
+        for ( ; ; )
+            halt();
     }
 }
 
-- 
1.7.10.4


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