[Xen-devel] [PATCH 2/2] x86/xen/64: Rearrange the SYSCALL entries

[Andy Lutomirski <luto@xxxxxxxxxx>]

Xen's raw SYSCALL entries are much less weird than native.  Rather
than fudging them to look like native entries, use the Xen-provided
stack frame directly.

This lets us eliminate entry_SYSCALL_64_after_swapgs and two uses
of the SWAPGS_UNSAFE_STACK paravirt hook.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/entry/entry_64.S        |  9 +--------
 arch/x86/entry/entry_64_compat.S |  2 +-
 arch/x86/xen/xen-asm_64.S        | 24 ++++++++++--------------
 3 files changed, 12 insertions(+), 23 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f47996910331..ebe7e2ca19fe 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -134,14 +134,7 @@ ENTRY(entry_SYSCALL_64)
         * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
         * it is too small to ever cause noticeable irq latency.
         */
-       SWAPGS_UNSAFE_STACK
-       /*
-        * A hypervisor implementation might want to use a label
-        * after the swapgs, so that it can do the swapgs
-        * for the guest and jump here on syscall.
-        */
-GLOBAL(entry_SYSCALL_64_after_swapgs)
-
+       swapgs
        movq    %rsp, PER_CPU_VAR(rsp_scratch)
        movq    PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index d39495d6446e..beae2b75b588 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -309,7 +309,7 @@ ENTRY(entry_SYSCALL_compat)
         * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
         * it is too small to ever cause noticeable irq latency.
         */
-       SWAPGS_UNSAFE_STACK
+       swapgs
        movl    %esp, %r8d
        movq    PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index f22667abf7b9..c2b5868a9967 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -100,34 +100,30 @@ RELOC(xen_sysret32, 1b+1)
  *     rip
  *     r11
  * rsp->rcx
- *
- * In all the entrypoints, we undo all that to make it look like a
- * CPU-generated syscall/sysenter and jump to the normal entrypoint.
  */
 
-.macro undo_xen_syscall
-       mov 0*8(%rsp), %rcx
-       mov 1*8(%rsp), %r11
-       mov 5*8(%rsp), %rsp
-.endm
-
 /* Normal 64-bit system call target */
 ENTRY(xen_syscall_target)
-       undo_xen_syscall
-       jmp entry_SYSCALL_64_after_swapgs
+       popq %rcx
+       popq %r11
+       jmp entry_SYSCALL_64_after_hwframe
 ENDPROC(xen_syscall_target)
 
 #ifdef CONFIG_IA32_EMULATION
 
 /* 32-bit compat syscall target */
 ENTRY(xen_syscall32_target)
-       undo_xen_syscall
-       jmp entry_SYSCALL_compat
+       popq %rcx
+       popq %r11
+       movl (3*8)(%rsp), %r8d          /* r8d = user esp */
+       jmp entry_SYSCALL_compat_after_hwframe_esp_in_r8d
 ENDPROC(xen_syscall32_target)
 
 /* 32-bit compat sysenter target */
 ENTRY(xen_sysenter_target)
-       undo_xen_syscall
+       mov 0*8(%rsp), %rcx
+       mov 1*8(%rsp), %r11
+       mov 5*8(%rsp), %rsp
        jmp entry_SYSENTER_compat
 ENDPROC(xen_sysenter_target)
 
-- 
2.4.3


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