Right now we have two IRET instructions that can fault for guest reasons, and
the pre exception table gives handle_exception as the fixup for both.
Instead, we can have compat_restore_all_guest() use restore_all_guest()'s IRET
which gives us just a single position to handle specially.
In exception_with_ints_disabled(), remove search_pre_exception_table() and use
a simpler check. Explain how the recovery works, because this isn't the first
time I've had to figure it out.
The reference to iret_to_guest highlights that any checking here is specific
to CONFIG_PV, so exclude it in !PV builds.
Later in exception_with_ints_disabled(), it suffices to load %ecx rather than
%rcx, and remove a stray semi-colon from the rep movsq.
No functional change.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
v2:
* New
---
xen/arch/x86/x86_64/compat/entry.S | 3 +--
xen/arch/x86/x86_64/entry.S | 31 ++++++++++++++++++++++--------
2 files changed, 24 insertions(+), 10 deletions(-)
diff --git a/xen/arch/x86/x86_64/compat/entry.S
b/xen/arch/x86/x86_64/compat/entry.S
index d7b381ea546d..39925d80a677 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -167,8 +167,7 @@ FUNC(compat_restore_all_guest)
scf=STK_REL(CPUINFO_scf, CPUINFO_rip), \
sel=STK_REL(CPUINFO_verw_sel, CPUINFO_rip)
-.Lft0: iretq
- _ASM_PRE_EXTABLE(.Lft0, handle_exception)
+ jmp iret_to_guest
END(compat_restore_all_guest)
/* Callers can cope with both %rax and %rcx being clobbered. */
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index c02245ac064c..01b431793b7b 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -241,8 +241,9 @@ iret_exit_to_guest:
SPEC_CTRL_COND_VERW /* Req: %rsp=eframe Clob:
efl */
addq $8,%rsp
-.Lft0: iretq
- _ASM_PRE_EXTABLE(.Lft0, handle_exception)
+
+LABEL(iret_to_guest, 0)
+ iretq
END(restore_all_guest)
/*
@@ -920,10 +921,23 @@ handle_exception_saved:
exception_with_ints_disabled:
testb $3,UREGS_cs(%rsp) # interrupts disabled outside Xen?
jnz FATAL_exception_with_ints_disabled
- movq %rsp,%rdi
- call search_pre_exception_table
- testq %rax,%rax # no fixup code for faulting EIP?
- jz .Ldispatch_exceptions
+
+#ifndef CONFIG_PV
+ /* No PV? No IRETs-to-guest to worry about. */
+ jmp .Ldispatch_exceptions
+#else
+ /* Check to see if the exception was on the IRET to guest context. */
+ lea iret_to_guest(%rip), %rax
+ cmp %rax, UREGS_rip(%rsp)
+ jne .Ldispatch_exceptions
+
+ /*
+ * Recovery is at handle_exception. It may be necessary to make space
+ * on the interrupted stack for ec/ev, after which the current ec/ev
+ * is copied to make it appear as if this exception occurred in guest
+ * context.
+ */
+ lea handle_exception(%rip), %rax
movq %rax,UREGS_rip(%rsp) # fixup regular stack
#ifdef CONFIG_XEN_SHSTK
@@ -940,13 +954,14 @@ exception_with_ints_disabled:
movq %rsp,%rsi
subq $8,%rsp
movq %rsp,%rdi
- movq $UREGS_kernel_sizeof/8,%rcx
- rep; movsq # make room for ec/ev
+ mov $UREGS_kernel_sizeof/8, %ecx
+ rep movsq # make room for ec/ev
1: movq UREGS_error_code(%rsp),%rax # ec/ev
movq %rax,UREGS_kernel_sizeof(%rsp)
mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
mov %r13b, STACK_CPUINFO_FIELD(use_pv_cr3)(%r14)
jmp restore_all_xen # return to fixup code
+#endif /* !CONFIG_PV */
/* No special register assumptions. */
FATAL_exception_with_ints_disabled:
--
2.39.5
