linux-kernel - [PATCH 11/11] x86/hyperv: Mark hv_ghcb

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Date:   Fri,  7 Apr 2023 17:10:04 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>, linux-btrfs@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        linux-scsi@...r.kernel.org, linux-hyperv@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Michael Kelley <mikelley@...rosoft.com>
Subject: [PATCH 11/11] x86/hyperv: Mark hv_ghcb_terminate() as noreturn

From: "Guilherme G. Piccoli" <gpiccoli@...lia.com>

Annotate the function prototype and definition as noreturn to prevent
objtool warnings like:

vmlinux.o: warning: objtool: hyperv_init+0x55c: unreachable instruction

Also, as per Josh's suggestion, add it to the global_noreturns list.
As a comparison, an objdump output without the annotation:

[...]
1b63:  mov    $0x1,%esi
1b68:  xor    %edi,%edi
1b6a:  callq  ffffffff8102f680 <hv_ghcb_terminate>
1b6f:  jmpq   ffffffff82f217ec <hyperv_init+0x9c> # unreachable
1b74:  cmpq   $0xffffffffffffffff,-0x702a24(%rip)
[...]

Now, after adding the __noreturn to the function prototype:

[...]
17df:  callq  ffffffff8102f6d0 <hv_ghcb_negotiate_protocol>
17e4:  test   %al,%al
17e6:  je     ffffffff82f21bb9 <hyperv_init+0x469>
[...]  <many insns>
1bb9:  mov    $0x1,%esi
1bbe:  xor    %edi,%edi
1bc0:  callq  ffffffff8102f680 <hv_ghcb_terminate>
1bc5:  nopw   %cs:0x0(%rax,%rax,1) # end of function

Reported-by: Arnd Bergmann <arnd@...db.de>
Link: https://lore.kernel.org/r/9698eff1-9680-4f0a-94de-590eaa923e94@app.fastmail.com/
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
Link: https://lore.kernel.org/r/20230317160546.1497477-1-gpiccoli@igalia.com
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/hyperv/ivm.c           | 2 +-
 arch/x86/include/asm/mshyperv.h | 2 +-
 tools/objtool/check.c           | 1 +
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 1dbcbd9da74d..4f79dc76042d 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -127,7 +127,7 @@ static enum es_result hv_ghcb_hv_call(struct ghcb *ghcb, u64 exit_code,
 		return ES_OK;
 }
 
-void hv_ghcb_terminate(unsigned int set, unsigned int reason)
+void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason)
 {
 	u64 val = GHCB_MSR_TERM_REQ;
 
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 4c4c0ec3b62e..09c26e658bcc 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -212,7 +212,7 @@ int hv_set_mem_host_visibility(unsigned long addr, int numpages, bool visible);
 void hv_ghcb_msr_write(u64 msr, u64 value);
 void hv_ghcb_msr_read(u64 msr, u64 *value);
 bool hv_ghcb_negotiate_protocol(void);
-void hv_ghcb_terminate(unsigned int set, unsigned int reason);
+void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason);
 #else
 static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
 static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8586d4c36600..e23d12041be0 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -213,6 +213,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"ex_handler_msr_mce",
 		"fortify_panic",
 		"hlt_play_dead",
+		"hv_ghcb_terminate",
 		"kthread_complete_and_exit",
 		"kthread_exit",
 		"kunit_try_catch_throw",
-- 
2.39.2