linux-kernel - [PATCH v3 10/13] x86/retpoline/pvops: Convert assembler indirect jumps

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Date:   Thu,  4 Jan 2018 14:37:07 +0000
From:   David Woodhouse <dwmw@...zon.co.uk>
To:     ak@...ux.intel.com
Cc:     David Woodhouse <dwmw@...zon.co.uk>, Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: [PATCH v3 10/13] x86/retpoline/pvops: Convert assembler indirect jumps

Convert pvops invocations to use non-speculative call sequences, when
CONFIG_RETPOLINE is enabled.

There is scope for future optimisation here — once the pvops methods are
actually set, we could just turn the damn things into *direct* jumps.
But this is perfectly sufficient for now, without that added complexity.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 arch/x86/include/asm/paravirt_types.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 6ec54d01972d..54b735b8ae12 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -336,11 +336,17 @@ extern struct pv_lock_ops pv_lock_ops;
 #define PARAVIRT_PATCH(x)					\
 	(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
 
+#define paravirt_clobber(clobber)		\
+	[paravirt_clobber] "i" (clobber)
+#ifdef CONFIG_RETPOLINE
+#define paravirt_type(op)				\
+	[paravirt_typenum] "i" (PARAVIRT_PATCH(op)),	\
+	[paravirt_opptr] "r" ((op))
+#else
 #define paravirt_type(op)				\
 	[paravirt_typenum] "i" (PARAVIRT_PATCH(op)),	\
 	[paravirt_opptr] "i" (&(op))
-#define paravirt_clobber(clobber)		\
-	[paravirt_clobber] "i" (clobber)
+#endif
 
 /*
  * Generate some code, and mark it as patchable by the
@@ -392,7 +398,11 @@ int paravirt_disable_iospace(void);
  * offset into the paravirt_patch_template structure, and can therefore be
  * freely converted back into a structure offset.
  */
+#ifdef CONFIG_RETPOLINE
+#define PARAVIRT_CALL	"call __x86.indirect_thunk.%V[paravirt_opptr];"
+#else
 #define PARAVIRT_CALL	"call *%c[paravirt_opptr];"
+#endif
 
 /*
  * These macros are intended to wrap calls through one of the paravirt
-- 
2.14.3