[tip: x86/entry] x86/xen: Unbreak hypervisor callback on 32bit

From: tip-bot2 for Thomas Gleixner
Date: Mon Jun 01 2020 - 17:36:53 EST

The following commit has been merged into the x86/entry branch of tip:

Commit-ID: 4b1f63084d3ebd14c3ef2cd4e8732c25bcd8381d
Gitweb: https://git.kernel.org/tip/4b1f63084d3ebd14c3ef2cd4e8732c25bcd8381d
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Mon, 01 Jun 2020 21:33:56 +02:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Mon, 01 Jun 2020 23:31:48 +02:00

x86/xen: Unbreak hypervisor callback on 32bit

The IDTENTRY conversion broke XEN on 32bit:

ld: arch/x86/xen/setup.o: in function `register_callback':
>> arch/x86/xen/setup.c:940: undefined reference to `xen_asm_exc_xen_hypervisor_callback'

The reason is that 32bit does not have the extra indirection of 64bit via
the XEN trampolines and 32bit never emitted an actual IDT entry function
for this.

- Add and use IDTENTRY_XENCB so the ASM variant emits an entry point only
for 64 bit.

- Rename the 32bit ASM function to match the 64bit trampoline function name.

Fixup a few comments as well.

Fixes: 66a07b44e765 ("x86/entry: Switch XEN/PV hypercall entry to IDTENTRY")
Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
---
arch/x86/entry/entry_32.S | 7 +++++--
arch/x86/include/asm/idtentry.h | 24 +++++++++++++++++++++++-
arch/x86/xen/xen-asm_32.S | 6 +++---
3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 96fa462..2d29f77 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1167,8 +1167,11 @@ SYM_CODE_END(native_iret)
#ifdef CONFIG_XEN_PV
/*
* See comment in entry_64.S for further explanation
+ *
+ * Note: This is not an actual IDT entry point. It's a XEN specific entry
+ * point and therefore named to match the 64-bit trampoline counterpart.
*/
-SYM_FUNC_START(exc_xen_hypervisor_callback)
+SYM_FUNC_START(xen_asm_exc_xen_hypervisor_callback)
/*
* Check to see if we got the event in the critical
* region in xen_iret_direct, after we've reenabled
@@ -1189,7 +1192,7 @@ SYM_FUNC_START(exc_xen_hypervisor_callback)
mov %esp, %eax
call xen_pv_evtchn_do_upcall
jmp handle_exception_return
-SYM_FUNC_END(exc_xen_hypervisor_callback)
+SYM_FUNC_END(xen_asm_exc_xen_hypervisor_callback)

/*
* Hypervisor uses this for application faults while it executes.
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index f8e2737..d203c54 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -283,6 +283,22 @@ __visible noinstr void func(struct pt_regs *regs) \
\
static __always_inline void __##func(struct pt_regs *regs)

+/**
+ * DECLARE_IDTENTRY_XENCB - Declare functions for XEN HV callback entry point
+ * @vector: Vector number (ignored for C)
+ * @func: Function name of the entry point
+ *
+ * Declares three functions:
+ * - The ASM entry point: asm_##func
+ * - The XEN PV trap entry point: xen_##func (maybe unused)
+ * - The C handler called from the ASM entry point
+ *
+ * Maps to DECLARE_IDTENTRY(). Distinct entry point to handle the 32/64-bit
+ * difference
+ */
+#define DECLARE_IDTENTRY_XENCB(vector, func) \
+ DECLARE_IDTENTRY(vector, func)
+
#ifdef CONFIG_X86_64
/**
* DECLARE_IDTENTRY_IST - Declare functions for IST handling IDT entry points
@@ -432,6 +448,9 @@ __visible noinstr void func(struct pt_regs *regs, \
# define DECLARE_IDTENTRY_DF(vector, func) \
idtentry_df vector asm_##func func

+# define DECLARE_IDTENTRY_XENCB(vector, func) \
+ DECLARE_IDTENTRY(vector, func)
+
#else
# define DECLARE_IDTENTRY_MCE(vector, func) \
DECLARE_IDTENTRY(vector, func)
@@ -442,6 +461,9 @@ __visible noinstr void func(struct pt_regs *regs, \
/* No ASM emitted for DF as this goes through a C shim */
# define DECLARE_IDTENTRY_DF(vector, func)

+/* No ASM emitted for XEN hypervisor callback */
+# define DECLARE_IDTENTRY_XENCB(vector, func)
+
#endif

/* No ASM code emitted for NMI */
@@ -558,7 +580,7 @@ DECLARE_IDTENTRY_XEN(X86_TRAP_DB, debug);
DECLARE_IDTENTRY_DF(X86_TRAP_DF, exc_double_fault);

#ifdef CONFIG_XEN_PV
-DECLARE_IDTENTRY(X86_TRAP_OTHER, exc_xen_hypervisor_callback);
+DECLARE_IDTENTRY_XENCB(X86_TRAP_OTHER, exc_xen_hypervisor_callback);
#endif

/* Device interrupts common/spurious */
diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S
index d0ff2dc..4757cec 100644
--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -113,7 +113,7 @@ iret_restore_end:
* Events are masked, so jumping out of the critical region is
* OK.
*/
- je asm_exc_xen_hypervisor_callback
+ je xen_asm_exc_xen_hypervisor_callback

1: iret
xen_iret_end_crit:
@@ -127,7 +127,7 @@ SYM_CODE_END(xen_iret)
.globl xen_iret_start_crit, xen_iret_end_crit

/*
- * This is called by exc_xen_hypervisor_callback in entry_32.S when it sees
+ * This is called by xen_asm_exc_xen_hypervisor_callback in entry_32.S when it sees
* that the EIP at the time of interrupt was between
* xen_iret_start_crit and xen_iret_end_crit.
*
@@ -144,7 +144,7 @@ SYM_CODE_END(xen_iret)
* eflags }
* cs } nested exception info
* eip }
- * return address : (into asm_exc_xen_hypervisor_callback)
+ * return address : (into xen_asm_exc_xen_hypervisor_callback)
*
* In order to deliver the nested exception properly, we need to discard the
* nested exception frame such that when we handle the exception, we do it