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 12:06:54 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 16.11.22 12:04, Peter Zijlstra wrote:
> 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?

Fine with me.

Thanks for looking at the patch,


Juergen

> 
> ---
> --- 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)
>   {


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