linux-kernel - Re: [PATCH v2] x86/paravirt: use common macro for creating simple asm paravirt functions

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Date:   Wed, 16 Nov 2022 12:04:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        "Srivatsa S. Bhat (VMware)" <srivatsa@...il.mit.edu>,
        Alexey Makhalov <amakhalov@...are.com>,
        VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH v2] x86/paravirt: use common macro for creating simple
 asm paravirt functions

On Wed, Nov 09, 2022 at 02:44:18PM +0100, Juergen Gross wrote:
> There are some paravirt assembler functions which are sharing a common
> pattern. Introduce a macro DEFINE_PARAVIRT_ASM() for creating them.
> 
> Note that this macro is including explicit alignment of the generated
> functions, leading to __raw_callee_save___kvm_vcpu_is_preempted(),
> _paravirt_nop() and paravirt_ret0() to be aligned at 4 byte boundaries
> now.
> 
> The explicit _paravirt_nop() prototype in paravirt.c isn't needed, as
> it is included in paravirt_types.h already.
> 
> Signed-off-by: Juergen Gross <jgross@...e.com>
> Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa@...il.mit.edu>
> ---

Seems nice; I've made the below little edits, but this is certainly a
bit large for /urgent at this point in time. So how about I merge
locking/urgent into x86/paravirt and munge this on top?

---
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -737,7 +737,7 @@ static __always_inline unsigned long arc
 	     __ALIGN_STR "\n"				\
 	     #func ":\n\t"				\
 	     ASM_ENDBR					\
-	     instr					\
+	     instr "\n\t"				\
 	     ASM_RET					\
 	     ".size " #func ", . - " #func "\n\t"	\
 	     ".popsection")
--- a/arch/x86/include/asm/qspinlock_paravirt.h
+++ b/arch/x86/include/asm/qspinlock_paravirt.h
@@ -54,8 +54,8 @@ __PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_
 	"pop    %rdx\n\t"						\
 	FRAME_END
 
-DEFINE_PARAVIRT_ASM(__raw_callee_save___pv_queued_spin_unlock, PV_UNLOCK_ASM,
-		    .spinlock.text);
+DEFINE_PARAVIRT_ASM(__raw_callee_save___pv_queued_spin_unlock,
+		    PV_UNLOCK_ASM, .spinlock.text);
 
 #else /* CONFIG_64BIT */
 
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -802,6 +802,7 @@ extern bool __raw_callee_save___kvm_vcpu
  "movq   __per_cpu_offset(,%rdi,8), %rax\n\t"				     \
  "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax)\n\t" \
  "setne  %al\n\t"
+
 DEFINE_PARAVIRT_ASM(__raw_callee_save___kvm_vcpu_is_preempted,
 		    PV_VCPU_PREEMPTED_ASM, .text);
 #endif
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -40,8 +40,7 @@
 DEFINE_PARAVIRT_ASM(_paravirt_nop, "", .entry.text);
 
 /* stub always returning 0. */
-#define PV_RET0_ASM	"xor %" _ASM_AX ", %" _ASM_AX "\n\t"
-DEFINE_PARAVIRT_ASM(paravirt_ret0, PV_RET0_ASM, .entry.text);
+DEFINE_PARAVIRT_ASM(paravirt_ret0, "xor %eax,%eax", .entry.text);
 
 void __init default_banner(void)
 {