linux-kernel - Re: [PATCH v5 19/43] KVM: arm64: Handle realm MMIO emulation

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Message-ID: <yq5awmik5yai.fsf@kernel.org>
Date: Mon, 07 Oct 2024 10:01:33 +0530
From: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
	kvmarm@...ts.linux.dev
Cc: Steven Price <steven.price@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Joey Gouly <joey.gouly@....com>,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
	Gavin Shan <gshan@...hat.com>,
	Shanker Donthineni <sdonthineni@...dia.com>,
	Alper Gun <alpergun@...gle.com>
Subject: Re: [PATCH v5 19/43] KVM: arm64: Handle realm MMIO emulation

Steven Price <steven.price@....com> writes:

> MMIO emulation for a realm cannot be done directly with the VM's
> registers as they are protected from the host. However, for emulatable
> data aborts, the RMM uses GPRS[0] to provide the read/written value.
> We can transfer this from/to the equivalent VCPU's register entry and
> then depend on the generic MMIO handling code in KVM.
>
> For a MMIO read, the value is placed in the shared RecExit structure
> during kvm_handle_mmio_return() rather than in the VCPU's register
> entry.
>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
> v3: Adapt to previous patch changes
> ---
>  arch/arm64/kvm/mmio.c     | 10 +++++++++-
>  arch/arm64/kvm/rme-exit.c |  6 ++++++
>  2 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c
> index cd6b7b83e2c3..66a838b3776a 100644
> --- a/arch/arm64/kvm/mmio.c
> +++ b/arch/arm64/kvm/mmio.c
> @@ -6,6 +6,7 @@
>  
>  #include <linux/kvm_host.h>
>  #include <asm/kvm_emulate.h>
> +#include <asm/rmi_smc.h>
>  #include <trace/events/kvm.h>
>  
>  #include "trace.h"
> @@ -90,6 +91,9 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu)
>  
>  	vcpu->mmio_needed = 0;
>  
> +	if (vcpu_is_rec(vcpu))
> +		vcpu->arch.rec.run->enter.flags |= REC_ENTER_EMULATED_MMIO;
> +
>  	if (!kvm_vcpu_dabt_iswrite(vcpu)) {
>  		struct kvm_run *run = vcpu->run;
>  
> @@ -108,7 +112,11 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu)
>  		trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr,
>  			       &data);
>  		data = vcpu_data_host_to_guest(vcpu, data, len);
> -		vcpu_set_reg(vcpu, kvm_vcpu_dabt_get_rd(vcpu), data);
> +
> +		if (vcpu_is_rec(vcpu))
> +			vcpu->arch.rec.run->enter.gprs[0] = data;
> +		else
> +			vcpu_set_reg(vcpu, kvm_vcpu_dabt_get_rd(vcpu), data);
>  	}
>  
>  	/*
>

Does a kvm_incr_pc(vcpu); make sense for realm guest? Should we do

modified   arch/arm64/kvm/mmio.c
@@ -91,9 +91,6 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu)
 
 	vcpu->mmio_needed = 0;
 
-	if (vcpu_is_rec(vcpu))
-		vcpu->arch.rec.run->enter.flags |= RMI_EMULATED_MMIO;
-
 	if (!kvm_vcpu_dabt_iswrite(vcpu)) {
 		struct kvm_run *run = vcpu->run;
 
@@ -123,7 +120,10 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu)
 	 * The MMIO instruction is emulated and should not be re-executed
 	 * in the guest.
 	 */
-	kvm_incr_pc(vcpu);
+	if (vcpu_is_rec(vcpu))
+		vcpu->arch.rec.run->enter.flags |= RMI_EMULATED_MMIO;
+	else
+		kvm_incr_pc(vcpu);
 
 	return 1;
 }



> diff --git a/arch/arm64/kvm/rme-exit.c b/arch/arm64/kvm/rme-exit.c
> index e96ea308212c..1ddbff123149 100644
> --- a/arch/arm64/kvm/rme-exit.c
> +++ b/arch/arm64/kvm/rme-exit.c
> @@ -25,6 +25,12 @@ static int rec_exit_reason_notimpl(struct kvm_vcpu *vcpu)
>  
>  static int rec_exit_sync_dabt(struct kvm_vcpu *vcpu)
>  {
> +	struct realm_rec *rec = &vcpu->arch.rec;
> +
> +	if (kvm_vcpu_dabt_iswrite(vcpu) && kvm_vcpu_dabt_isvalid(vcpu))
> +		vcpu_set_reg(vcpu, kvm_vcpu_dabt_get_rd(vcpu),
> +			     rec->run->exit.gprs[0]);
> +
>  	return kvm_handle_guest_abort(vcpu);
>  }
>  
> -- 
> 2.34.1