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Date: Tue, 8 Nov 2022 21:16:34 -0800
From: "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
To: Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
x86@...nel.org, virtualization@...ts.linux-foundation.org,
kvm@...r.kernel.org
Cc: 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] x86/paravirt: use common macro for creating simple asm
paravirt functions
Hi Juergen,
Sorry for the delay in reviewing this patch!
On 10/20/22 2:19 AM, Juergen Gross wrote:
> There are some paravirt assembler functions which are sharing a common
> pattern. Introduce a macro DEFINE_PARAVIRT_ASM() for creating them.
>
> 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>
I just wanted to make a note that the part of this patch that's not
purely cleanup is the addition of the alignment (__ALIGN_STR) to
__raw_callee_save___kvm_vcpu_is_preempted(), _paravirt_nop() and
paravirt_ret0(). Maybe that's worth calling out in the commit message?
Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa@...il.mit.edu>
Regards,
Srivatsa
VMware Photon OS
> ---
> arch/x86/include/asm/paravirt.h | 12 ++++++
> arch/x86/include/asm/qspinlock_paravirt.h | 46 ++++++++++-------------
> arch/x86/kernel/kvm.c | 19 +++-------
> arch/x86/kernel/paravirt.c | 22 ++---------
> 4 files changed, 40 insertions(+), 59 deletions(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 2a0b8dd4ec33..479bf264b8aa 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -730,6 +730,18 @@ static __always_inline unsigned long arch_local_irq_save(void)
> #undef PVOP_VCALL4
> #undef PVOP_CALL4
>
> +#define DEFINE_PARAVIRT_ASM(func, instr, sec) \
> + asm (".pushsection " #sec ", \"ax\"\n" \
> + ".global " #func "\n\t" \
> + ".type " #func ", @function\n\t" \
> + __ALIGN_STR "\n" \
> + #func ":\n\t" \
> + ASM_ENDBR \
> + instr \
> + ASM_RET \
> + ".size " #func ", . - " #func "\n\t" \
> + ".popsection")
> +
> extern void default_banner(void);
>
> #else /* __ASSEMBLY__ */
> diff --git a/arch/x86/include/asm/qspinlock_paravirt.h b/arch/x86/include/asm/qspinlock_paravirt.h
> index 60ece592b220..c490f5eb9f3e 100644
> --- a/arch/x86/include/asm/qspinlock_paravirt.h
> +++ b/arch/x86/include/asm/qspinlock_paravirt.h
> @@ -14,8 +14,6 @@
>
> __PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath, ".spinlock.text");
> #define __pv_queued_spin_unlock __pv_queued_spin_unlock
> -#define PV_UNLOCK "__raw_callee_save___pv_queued_spin_unlock"
> -#define PV_UNLOCK_SLOWPATH "__raw_callee_save___pv_queued_spin_unlock_slowpath"
>
> /*
> * Optimized assembly version of __raw_callee_save___pv_queued_spin_unlock
> @@ -37,32 +35,26 @@ __PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath, ".spinlock.text");
> * rsi = lockval (second argument)
> * rdx = internal variable (set to 0)
> */
> -asm (".pushsection .spinlock.text;"
> - ".globl " PV_UNLOCK ";"
> - ".type " PV_UNLOCK ", @function;"
> - ".align 4,0x90;"
> - PV_UNLOCK ": "
> - ASM_ENDBR
> - FRAME_BEGIN
> - "push %rdx;"
> - "mov $0x1,%eax;"
> - "xor %edx,%edx;"
> - LOCK_PREFIX "cmpxchg %dl,(%rdi);"
> - "cmp $0x1,%al;"
> - "jne .slowpath;"
> - "pop %rdx;"
> +#define PV_UNLOCK_ASM \
> + FRAME_BEGIN \
> + "push %rdx\n\t" \
> + "mov $0x1,%eax\n\t" \
> + "xor %edx,%edx\n\t" \
> + LOCK_PREFIX "cmpxchg %dl,(%rdi)\n\t" \
> + "cmp $0x1,%al\n\t" \
> + "jne .slowpath\n\t" \
> + "pop %rdx\n\t" \
> + FRAME_END \
> + ASM_RET \
> + ".slowpath:\n\t" \
> + "push %rsi\n\t" \
> + "movzbl %al,%esi\n\t" \
> + "call __raw_callee_save___pv_queued_spin_unlock_slowpath\n\t" \
> + "pop %rsi\n\t" \
> + "pop %rdx\n\t" \
> FRAME_END
> - ASM_RET
> - ".slowpath: "
> - "push %rsi;"
> - "movzbl %al,%esi;"
> - "call " PV_UNLOCK_SLOWPATH ";"
> - "pop %rsi;"
> - "pop %rdx;"
> - FRAME_END
> - ASM_RET
> - ".size " PV_UNLOCK ", .-" PV_UNLOCK ";"
> - ".popsection");
> +DEFINE_PARAVIRT_ASM(__raw_callee_save___pv_queued_spin_unlock, PV_UNLOCK_ASM,
> + .spinlock.text);
>
> #else /* CONFIG_64BIT */
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index d4e48b4a438b..856708cc78e7 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -798,19 +798,12 @@ 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.
> */
> -asm(
> -".pushsection .text;"
> -".global __raw_callee_save___kvm_vcpu_is_preempted;"
> -".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
> -"__raw_callee_save___kvm_vcpu_is_preempted:"
> -ASM_ENDBR
> -"movq __per_cpu_offset(,%rdi,8), %rax;"
> -"cmpb $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax);"
> -"setne %al;"
> -ASM_RET
> -".size __raw_callee_save___kvm_vcpu_is_preempted, .-__raw_callee_save___kvm_vcpu_is_preempted;"
> -".popsection");
> -
> +#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" \
> + "setne %al\n\t"
> +DEFINE_PARAVIRT_ASM(__raw_callee_save___kvm_vcpu_is_preempted,
> + PV_VCPU_PREEMPTED_ASM, .text);
> #endif
>
> static void __init kvm_guest_init(void)
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index 7ca2d46c08cc..6f306f885caf 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -37,27 +37,11 @@
> * nop stub, which must not clobber anything *including the stack* to
> * avoid confusing the entry prologues.
> */
> -extern void _paravirt_nop(void);
> -asm (".pushsection .entry.text, \"ax\"\n"
> - ".global _paravirt_nop\n"
> - "_paravirt_nop:\n\t"
> - ASM_ENDBR
> - ASM_RET
> - ".size _paravirt_nop, . - _paravirt_nop\n\t"
> - ".type _paravirt_nop, @function\n\t"
> - ".popsection");
> +DEFINE_PARAVIRT_ASM(_paravirt_nop, "", .entry.text);
>
> /* stub always returning 0. */
> -asm (".pushsection .entry.text, \"ax\"\n"
> - ".global paravirt_ret0\n"
> - "paravirt_ret0:\n\t"
> - ASM_ENDBR
> - "xor %" _ASM_AX ", %" _ASM_AX ";\n\t"
> - ASM_RET
> - ".size paravirt_ret0, . - paravirt_ret0\n\t"
> - ".type paravirt_ret0, @function\n\t"
> - ".popsection");
> -
> +#define PV_RET0_ASM "xor %" _ASM_AX ", %" _ASM_AX "\n\t"
> +DEFINE_PARAVIRT_ASM(paravirt_ret0, PV_RET0_ASM, .entry.text);
>
> void __init default_banner(void)
> {
>
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