Re: [PATCH v3 05/16] perf: Drop dead and useless guest "support" from arm, csky, nds32 and riscv

From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Marc Zyngier <maz@kernel.org>, Guo Ren <guoren@kernel.org>,
	Nick Hu <nickhu@andestech.com>, Greentime Hu <green.hu@gmail.com>,
	Vincent Chen <deanbo422@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvmarm@lists.cs.columbia.edu, linux-csky@vger.kernel.org,
	linux-riscv@lists.infradead.org, kvm@vger.kernel.org,
	xen-devel@lists.xenproject.org,
	Artem Kashkanov <artem.kashkanov@intel.com>,
	Like Xu <like.xu.linux@gmail.com>,
	Zhu Lingshan <lingshan.zhu@intel.com>
Subject: Re: [PATCH v3 05/16] perf: Drop dead and useless guest "support" from arm, csky, nds32 and riscv
Date: Wed, 22 Sep 2021 08:26:29 +0200	[thread overview]
Message-ID: <2462bc44-64a5-8bac-7c3c-d837c4b3f743@redhat.com> (raw)
In-Reply-To: <20210922000533.713300-6-seanjc@google.com>

On 22/09/21 02:05, Sean Christopherson wrote:
> Drop "support" for guest callbacks from architctures that don't implement
> the guest callbacks.  Future patches will convert the callbacks to
> static_call; rather than churn a bunch of arch code (that was presumably
> copy+pasted from x86), remove it wholesale as it's useless and at best
> wasting cycles.
> 
> A future patch will also add a Kconfig to force architcture to opt into
> the callbacks to make it more difficult for uses "support" to sneak in in
> the future.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/arm/kernel/perf_callchain.c   | 33 ++++-------------------------
>   arch/csky/kernel/perf_callchain.c  | 12 -----------
>   arch/nds32/kernel/perf_event_cpu.c | 34 ++++--------------------------
>   arch/riscv/kernel/perf_callchain.c | 13 ------------
>   4 files changed, 8 insertions(+), 84 deletions(-)
> 
> diff --git a/arch/arm/kernel/perf_callchain.c b/arch/arm/kernel/perf_callchain.c
> index 1626dfc6f6ce..bc6b246ab55e 100644
> --- a/arch/arm/kernel/perf_callchain.c
> +++ b/arch/arm/kernel/perf_callchain.c
> @@ -62,14 +62,8 @@ user_backtrace(struct frame_tail __user *tail,
>   void
>   perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	struct frame_tail __user *tail;
>   
> -	if (guest_cbs && guest_cbs->is_in_guest()) {
> -		/* We don't support guest os callchain now */
> -		return;
> -	}
> -
>   	perf_callchain_store(entry, regs->ARM_pc);
>   
>   	if (!current->mm)
> @@ -99,44 +93,25 @@ callchain_trace(struct stackframe *fr,
>   void
>   perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	struct stackframe fr;
>   
> -	if (guest_cbs && guest_cbs->is_in_guest()) {
> -		/* We don't support guest os callchain now */
> -		return;
> -	}
> -
>   	arm_get_current_stackframe(regs, &fr);
>   	walk_stackframe(&fr, callchain_trace, entry);
>   }
>   
>   unsigned long perf_instruction_pointer(struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> -
> -	if (guest_cbs && guest_cbs->is_in_guest())
> -		return guest_cbs->get_guest_ip();
> -
>   	return instruction_pointer(regs);
>   }
>   
>   unsigned long perf_misc_flags(struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	int misc = 0;
>   
> -	if (guest_cbs && guest_cbs->is_in_guest()) {
> -		if (guest_cbs->is_user_mode())
> -			misc |= PERF_RECORD_MISC_GUEST_USER;
> -		else
> -			misc |= PERF_RECORD_MISC_GUEST_KERNEL;
> -	} else {
> -		if (user_mode(regs))
> -			misc |= PERF_RECORD_MISC_USER;
> -		else
> -			misc |= PERF_RECORD_MISC_KERNEL;
> -	}
> +	if (user_mode(regs))
> +		misc |= PERF_RECORD_MISC_USER;
> +	else
> +		misc |= PERF_RECORD_MISC_KERNEL;
>   
>   	return misc;
>   }
> diff --git a/arch/csky/kernel/perf_callchain.c b/arch/csky/kernel/perf_callchain.c
> index 35318a635a5f..92057de08f4f 100644
> --- a/arch/csky/kernel/perf_callchain.c
> +++ b/arch/csky/kernel/perf_callchain.c
> @@ -86,13 +86,8 @@ static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
>   void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
>   			 struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	unsigned long fp = 0;
>   
> -	/* C-SKY does not support virtualization. */
> -	if (guest_cbs && guest_cbs->is_in_guest())
> -		return;
> -
>   	fp = regs->regs[4];
>   	perf_callchain_store(entry, regs->pc);
>   
> @@ -111,15 +106,8 @@ void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
>   void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
>   			   struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	struct stackframe fr;
>   
> -	/* C-SKY does not support virtualization. */
> -	if (guest_cbs && guest_cbs->is_in_guest()) {
> -		pr_warn("C-SKY does not support perf in guest mode!");
> -		return;
> -	}
> -
>   	fr.fp = regs->regs[4];
>   	fr.lr = regs->lr;
>   	walk_stackframe(&fr, entry);
> diff --git a/arch/nds32/kernel/perf_event_cpu.c b/arch/nds32/kernel/perf_event_cpu.c
> index f38791960781..a78a879e7ef1 100644
> --- a/arch/nds32/kernel/perf_event_cpu.c
> +++ b/arch/nds32/kernel/perf_event_cpu.c
> @@ -1363,7 +1363,6 @@ void
>   perf_callchain_user(struct perf_callchain_entry_ctx *entry,
>   		    struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	unsigned long fp = 0;
>   	unsigned long gp = 0;
>   	unsigned long lp = 0;
> @@ -1372,11 +1371,6 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry,
>   
>   	leaf_fp = 0;
>   
> -	if (guest_cbs && guest_cbs->is_in_guest()) {
> -		/* We don't support guest os callchain now */
> -		return;
> -	}
> -
>   	perf_callchain_store(entry, regs->ipc);
>   	fp = regs->fp;
>   	gp = regs->gp;
> @@ -1480,13 +1474,8 @@ void
>   perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
>   		      struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	struct stackframe fr;
>   
> -	if (guest_cbs && guest_cbs->is_in_guest()) {
> -		/* We don't support guest os callchain now */
> -		return;
> -	}
>   	fr.fp = regs->fp;
>   	fr.lp = regs->lp;
>   	fr.sp = regs->sp;
> @@ -1495,32 +1484,17 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
>   
>   unsigned long perf_instruction_pointer(struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> -
> -	/* However, NDS32 does not support virtualization */
> -	if (guest_cbs && guest_cbs->is_in_guest())
> -		return guest_cbs->get_guest_ip();
> -
>   	return instruction_pointer(regs);
>   }
>   
>   unsigned long perf_misc_flags(struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	int misc = 0;
>   
> -	/* However, NDS32 does not support virtualization */
> -	if (guest_cbs && guest_cbs->is_in_guest()) {
> -		if (guest_cbs->is_user_mode())
> -			misc |= PERF_RECORD_MISC_GUEST_USER;
> -		else
> -			misc |= PERF_RECORD_MISC_GUEST_KERNEL;
> -	} else {
> -		if (user_mode(regs))
> -			misc |= PERF_RECORD_MISC_USER;
> -		else
> -			misc |= PERF_RECORD_MISC_KERNEL;
> -	}
> +	if (user_mode(regs))
> +		misc |= PERF_RECORD_MISC_USER;
> +	else
> +		misc |= PERF_RECORD_MISC_KERNEL;
>   
>   	return misc;
>   }
> diff --git a/arch/riscv/kernel/perf_callchain.c b/arch/riscv/kernel/perf_callchain.c
> index 8ecfc4c128bc..1fc075b8f764 100644
> --- a/arch/riscv/kernel/perf_callchain.c
> +++ b/arch/riscv/kernel/perf_callchain.c
> @@ -56,13 +56,8 @@ static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
>   void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
>   			 struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	unsigned long fp = 0;
>   
> -	/* RISC-V does not support perf in guest mode. */
> -	if (guest_cbs && guest_cbs->is_in_guest())
> -		return;
> -
>   	fp = regs->s0;
>   	perf_callchain_store(entry, regs->epc);
>   
> @@ -79,13 +74,5 @@ static bool fill_callchain(void *entry, unsigned long pc)
>   void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
>   			   struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> -
> -	/* RISC-V does not support perf in guest mode. */
> -	if (guest_cbs && guest_cbs->is_in_guest()) {
> -		pr_warn("RISC-V does not support perf in guest mode!");
> -		return;
> -	}
> -
>   	walk_stackframe(NULL, regs, fill_callchain, entry);
>   }
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>