[Xen-devel] [PATCH 1/6] x86/suspend: Clarify and improve the behaviour of do_suspend_lowlevel()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

do_suspend_lowlevel() behaves as a function call, even when the trampoline
jumps back into the middle of it.  Discuss this property, while renaming the
far-too-generic __ret_point to s3_resume.

Optimise the calling logic for acpi_enter_sleep_state().  $3 doesn't require a
64bit write, and the function isn't variadic so doesn't need to specify zero
FPU registers in use.

In the case of an acpi_enter_sleep_state() error, we didn't actually lose
state so don't need to restore it.  Jump straight to the end.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/acpi/wakeup_prot.S | 23 ++++++++++++++++-------
 xen/arch/x86/boot/wakeup.S      |  2 +-
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/acpi/wakeup_prot.S b/xen/arch/x86/acpi/wakeup_prot.S
index 74261cb4f1..8c525a802b 100644
--- a/xen/arch/x86/acpi/wakeup_prot.S
+++ b/xen/arch/x86/acpi/wakeup_prot.S
@@ -42,15 +42,23 @@ ENTRY(do_suspend_lowlevel)
 
         call    save_rest_processor_state
 
-        mov     $3, %rdi
-        xor     %eax, %eax
-
         /* enter sleep state physically */
+        mov     $3, %edi
         call    acpi_enter_sleep_state
-        jmp     __ret_point
-
 
-ENTRY(__ret_point)
+        /* It seems we didn't suspend.  Get out of here. */
+        jmp     .Lsuspend_err
+
+        /*
+         * do_suspend_lowlevel() is arranged to behave as a regular function
+         * call, even if hardware actually goes to sleep in the middle.
+         *
+         * The trampoline re-intercepts here.  State is:
+         *  - 64bit mode
+         *
+         * Everything else, including the stack, needs restoring.
+         */
+ENTRY(s3_resume)
         lgdt    boot_gdtr(%rip)
 
         /* mmu_cr4_features contains latest cr4 setting */
@@ -92,7 +100,8 @@ ENTRY(__ret_point)
         LOAD_GREG(13)
         LOAD_GREG(14)
         LOAD_GREG(15)
-        ret 
+.Lsuspend_err:
+        ret
 
 .data
         .align 16
diff --git a/xen/arch/x86/boot/wakeup.S b/xen/arch/x86/boot/wakeup.S
index fc47721f43..c17d613b61 100644
--- a/xen/arch/x86/boot/wakeup.S
+++ b/xen/arch/x86/boot/wakeup.S
@@ -151,7 +151,7 @@ wakeup_32:
         .code64
 wakeup_64:
         /* Jump to high mappings and the higher-level wakeup code. */
-        movabs  $__ret_point, %rbx
+        movabs  $s3_resume, %rbx
         jmp     *%rbx
 
 bogus_saved_magic:
-- 
2.11.0


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