linux-kernel - [PATCH RESEND] x86-64: use RIP-relative calls for paravirt indirect ones

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Date:   Wed, 15 Aug 2018 02:09:26 -0600
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "the arch/x86 maintainers" <x86@...nel.org>,
        "Juergen Gross" <jgross@...e.com>,
        "Alok Kataria" <akataria@...are.com>
Cc:     "Linux Virtualization" <virtualization@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: [PATCH RESEND] x86-64: use RIP-relative calls for paravirt
 indirect ones

This saves one insn byte per instance, summing up to a savings of over
4k in my (stripped down) configuration. No variant of to be patched in
replacement code relies on the one byte larger size.

Signed-off-by: Jan Beulich <jbeulich@...e.com>
Reviewed-by: Juergen Gross <jgross@...e.com>
---
Resend to include x86 maintainers, who aren't listed explicitly for the
file changed.
---
 arch/x86/include/asm/paravirt_types.h |    6 ++++++
 1 file changed, 6 insertions(+)

--- 4.18/arch/x86/include/asm/paravirt_types.h
+++ 4.18-x86_64-pvops-call-RIPrel/arch/x86/include/asm/paravirt_types.h
@@ -393,9 +393,15 @@ 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_X86_32
 #define PARAVIRT_CALL					\
 	ANNOTATE_RETPOLINE_SAFE				\
 	"call *%c[paravirt_opptr];"
+#else
+#define PARAVIRT_CALL					\
+	ANNOTATE_RETPOLINE_SAFE				\
+	"call *%c[paravirt_opptr](%%rip);"
+#endif
 
 /*
  * These macros are intended to wrap calls through one of the paravirt