Re: [PATCH v3 16/18] KVM: arm64: nVHE: Migrate hyp interface to SMCCC

From: Andrew Scull <ascull@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kernel-team@android.com, suzuki.poulose@arm.com,
	catalin.marinas@arm.com, james.morse@arm.com,
	linux-arm-kernel@lists.infradead.org,
	Sudeep Holla <sudeep.holla@arm.com>,
	David Brazdil <dbrazdil@google.com>,
	will@kernel.org, kvmarm@lists.cs.columbia.edu,
	julien.thierry.kdev@gmail.com
Subject: Re: [PATCH v3 16/18] KVM: arm64: nVHE: Migrate hyp interface to SMCCC
Date: Tue, 8 Sep 2020 12:02:22 +0100	[thread overview]
Message-ID: <20200908110222.GF3268721@google.com> (raw)
In-Reply-To: <87o8mhlld4.wl-maz@kernel.org>

On Mon, Sep 07, 2020 at 03:20:07PM +0100, Marc Zyngier wrote:
> On Thu, 03 Sep 2020 14:53:05 +0100,
> Andrew Scull <ascull@google.com> wrote:
> > 
> > Rather than passing arbitrary function pointers to run at hyp, define
> > and equivalent set of SMCCC functions.
> > 
> > Since the SMCCC functions are strongly tied to the original function
> > prototypes, it is not expected for the host to ever call an invalid ID
> > but a warning is raised if this does ever occur.
> > 
> > As __kvm_vcpu_run is used for every switch between the host and a guest,
> > it is explicitly singled out to be identified before the other function
> > IDs to improve the performance of the hot path.
> > 
> > Signed-off-by: Andrew Scull <ascull@google.com>
> > Signed-off-by: David Brazdil <dbrazdil@google.com>
> > ---
> >  arch/arm64/include/asm/kvm_asm.h   |  24 ++++++
> >  arch/arm64/include/asm/kvm_host.h  |  25 ++++---
> >  arch/arm64/kvm/arm.c               |   2 +-
> >  arch/arm64/kvm/hyp.S               |  24 ++----
> >  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 113 +++++++++++++++++++++++++----
> >  5 files changed, 145 insertions(+), 43 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> > index 4bbde3d3989c..4a73f1349151 100644
> > --- a/arch/arm64/include/asm/kvm_asm.h
> > +++ b/arch/arm64/include/asm/kvm_asm.h
> > @@ -38,6 +38,30 @@
> >  
> >  #define __SMCCC_WORKAROUND_1_SMC_SZ 36
> >  
> > +#define KVM_HOST_SMCCC_ID(id)						\
> > +	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
> > +			   ARM_SMCCC_SMC_64,				\
> > +			   ARM_SMCCC_OWNER_STANDARD_HYP,		\
> > +			   (id))
> > +
> > +#define KVM_HOST_SMCCC_FUNC(name) KVM_HOST_SMCCC_ID(__KVM_HOST_SMCCC_FUNC_##name)
> > +
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_hyp_init			0
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_flush_vm_context		1
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid_ipa		2
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid		3
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_local_vmid	4
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_timer_set_cntvoff		5
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_vcpu_run			6
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_enable_ssbs			7
> > +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_get_ich_vtr_el2		8
> > +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_read_vmcr		9
> > +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_write_vmcr		10
> > +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_init_lrs		11
> > +#define __KVM_HOST_SMCCC_FUNC___kvm_get_mdcr_el2		12
> > +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs		13
> > +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs		14
> 
> Wait. This looks broken. How do you distinguish between these and the
> stubs?

The __KVM_HOST_SMCCC_FUNC_* definitions are just the function ID part of
the SMCCC x0 argument. KVM_HOST_SMCCC_ID builds it into a 64-bit
fastcall owner by the hypervisor. The stubs fall into the legacy region
so these don't conflict.

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