[PATCH v2 2/4] x86/trampoline: Simplify the wakeup_stack checks

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

By checking that the permanent trampoline fits within 1k (at the time of
writing, it's 0x229 bytes), we can simplify the wakeup_stack handling.

Move the setup into wakeup.S, because it's rather out of place in
trampoline.S, and change it to a local symbol.

Drop wakeup_stack_start and WAKEUP_STACK_MIN entirely.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
CC: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
CC: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>

v2:
 * New
---
 xen/arch/x86/boot/trampoline.S    | 5 -----
 xen/arch/x86/boot/wakeup.S        | 8 +++++---
 xen/arch/x86/include/asm/config.h | 2 --
 xen/arch/x86/xen.lds.S            | 7 ++++---
 4 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 55e4a3e402f7..924bda37c1b7 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -156,11 +156,6 @@ GLOBAL(trampoline_xen_phys_start)
 GLOBAL(trampoline_cpu_started)
         .byte   0
 
-/* The first page of trampoline is permanent, the rest boot-time only. */
-/* Reuse the boot trampoline on the 1st trampoline page as stack for wakeup. */
-        .equ    wakeup_stack, trampoline_start + PAGE_SIZE
-        .global wakeup_stack
-
 LABEL(trampoline_perm_end, 0)
 
 /* From here on early boot only. */
diff --git a/xen/arch/x86/boot/wakeup.S b/xen/arch/x86/boot/wakeup.S
index df5ea2445739..d53f92b02463 100644
--- a/xen/arch/x86/boot/wakeup.S
+++ b/xen/arch/x86/boot/wakeup.S
@@ -1,5 +1,10 @@
         .code16
 
+/* The first page of trampoline is permanent, the rest boot-time only. */
+/* Reuse the boot logic on the first trampoline page as stack for wakeup. */
+        .equ    wakeup_stack, trampoline_start + PAGE_SIZE
+        .local  wakeup_stack
+
 #define wakesym(sym) (sym - wakeup_start)
 
 /*
@@ -166,6 +171,3 @@ wakeup_64:
         /* Jump to high mappings and the higher-level wakeup code. */
         movabs  $s3_resume, %rbx
         jmp     *%rbx
-
-/* Stack for wakeup: rest of first trampoline page. */
-ENTRY(wakeup_stack_start)
diff --git a/xen/arch/x86/include/asm/config.h 
b/xen/arch/x86/include/asm/config.h
index f8a5a4913b07..84696e0a7db5 100644
--- a/xen/arch/x86/include/asm/config.h
+++ b/xen/arch/x86/include/asm/config.h
@@ -53,8 +53,6 @@
 
 #define TRAMPOLINE_STACK_SPACE  PAGE_SIZE
 #define TRAMPOLINE_SPACE        (KB(64) - TRAMPOLINE_STACK_SPACE)
-#define WAKEUP_STACK_MIN        3072
-
 #define MBI_SPACE_MIN           (2 * PAGE_SIZE)
 
 /* Primary stack is restricted to 8kB by guard pages. */
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 221fc2ef3f35..224b46771d0c 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -413,11 +413,12 @@ ASSERT(!SIZEOF(.rela),     "leftover relocations")
 /*
  * The permanent trampoline resides in a single 4k page.  Placement logic
  * takes care to ensure that trampoline_phys is page aligned.
+ *
+ * The wakeup stack wants to reside in the same page and wants to be at least
+ * 3k in size, so make sure the text/data fits in 1k.
  */
-ASSERT((trampoline_perm_end - trampoline_start) <= PAGE_SIZE,
+ASSERT((trampoline_perm_end - trampoline_start) <= 1024,
        "Permentant trampoline too large")
 
 ASSERT((trampoline_end - trampoline_start) < TRAMPOLINE_SPACE - MBI_SPACE_MIN,
     "not enough room for trampoline and mbi data")
-ASSERT((wakeup_stack - wakeup_stack_start) >= WAKEUP_STACK_MIN,
-    "wakeup stack too small")
-- 
2.39.5