linux-kernel - Re: [PATCH v8 21/28] KVM: arm64: Add tracing capability for the pKVM hyp

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Message-ID: <aSWRdSELuYpAXCM8@google.com>
Date: Tue, 25 Nov 2025 11:22:29 +0000
From: Vincent Donnefort <vdonnefort@...gle.com>
To: Marc Zyngier <maz@...nel.org>
Cc: rostedt@...dmis.org, mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com, linux-trace-kernel@...r.kernel.org,
	oliver.upton@...ux.dev, joey.gouly@....com, suzuki.poulose@....com,
	yuzenghui@...wei.com, kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, jstultz@...gle.com,
	qperret@...gle.com, will@...nel.org, aneesh.kumar@...nel.org,
	kernel-team@...roid.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 21/28] KVM: arm64: Add tracing capability for the pKVM
 hyp

[...]

> > diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> > index f55a9a17d38f..504c3b9caef8 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> > +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> > @@ -29,7 +29,7 @@ hyp-obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
> >  	 ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
> >  hyp-obj-y += ../../../kernel/smccc-call.o
> >  hyp-obj-$(CONFIG_LIST_HARDENED) += list_debug.o
> > -hyp-obj-$(CONFIG_PKVM_TRACING) += clock.o
> > +hyp-obj-$(CONFIG_PKVM_TRACING) += clock.o trace.o ../../../../../kernel/trace/simple_ring_buffer.o
> 
> Can we get something less awful here? Surely there is a way to get an
> absolute path from the kbuild infrastructure? $(objtree) springs to
> mind...

Because of the path substitution below, I can't simply use $(objtree) here. I
suppose that's why all other paths above are relative.

However, I could probably simplify by including simple_ring_buffer.c into trace.c:

  diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
  -hyp-obj-$(CONFIG_TRACING) += clock.o trace.o ../../../../../kernel/trace/simple_ring_buffer.o
  +hyp-obj-$(CONFIG_TRACING) += clock.o trace.o
   hyp-obj-y += $(lib-objs)
   
  +# Path to simple_ring_buffer.c
  +CFLAGS_trace.nvhe.o += -I$(objtree)/kernel/trace/
  +
  
  
  diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
  -#include <linux/simple_ring_buffer.h>
  +#include "simple_ring_buffer.c"

> 
> >  hyp-obj-y += $(lib-objs)
> >  
> >  ##
> > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c

[...]