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

From: Peter Zijlstra
Date: Wed Nov 16 2022 - 06:18:16 EST


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@xxxxxxxx>
> Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa@xxxxxxxxxxxxx>
> ---

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)
{