linux-kernel - [RFC PATCH 13/28] x86/kvm: Use RIP-relative addressing

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Message-ID: <20240925150059.3955569-43-ardb+git@google.com>
Date: Wed, 25 Sep 2024 17:01:13 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Uros Bizjak <ubizjak@...il.com>, 
	Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>, 
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	Vitaly Kuznetsov <vkuznets@...hat.com>, Juergen Gross <jgross@...e.com>, 
	Boris Ostrovsky <boris.ostrovsky@...cle.com>, 
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	Masahiro Yamada <masahiroy@...nel.org>, Kees Cook <kees@...nel.org>, 
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	Kan Liang <kan.liang@...ux.intel.com>, linux-doc@...r.kernel.org, 
	linux-pm@...r.kernel.org, kvm@...r.kernel.org, xen-devel@...ts.xenproject.org, 
	linux-efi@...r.kernel.org, linux-arch@...r.kernel.org, 
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	llvm@...ts.linux.dev
Subject: [RFC PATCH 13/28] x86/kvm: Use RIP-relative addressing

From: Ard Biesheuvel <ardb@...nel.org>

Avoid absolute references in code, which require fixing up at boot time,
and replace them with RIP-relative ones. In this particular case, due to
the register pressure, they cannot be avoided entirely, so one absolute
reference is retained but the resulting reference via the GOT is
compatible with running the linker in PIE mode.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/kernel/kvm.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 263f8aed4e2c..8eac209a31aa 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -800,9 +800,11 @@ extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
  * Hand-optimize version for x86-64 to avoid 8 64-bit register saving and
  * restoring to/from the stack.
  */
-#define PV_VCPU_PREEMPTED_ASM						     \
- "movq   __per_cpu_offset(,%rdi,8), %rax\n\t"				     \
- "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax)\n\t" \
+#define PV_VCPU_PREEMPTED_ASM						\
+ "leaq   __per_cpu_offset(%rip), %rax				\n\t"	\
+ "movq   (%rax,%rdi,8), %rax					\n\t"	\
+ "addq   steal_time@...PCREL(%rip), %rax			\n\t"	\
+ "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "(%rax)	\n\t"	\
  "setne  %al\n\t"
 
 DEFINE_ASM_FUNC(__raw_callee_save___kvm_vcpu_is_preempted,
-- 
2.46.0.792.g87dc391469-goog