On 07/10/2024 05:31, Aneesh Kumar K.V wrote:
> Steven Price <steven.price@xxxxxxx> 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@xxxxxxx>
>> ---
>> 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
The PC is ignored when restarting realm guest, so kvm_incr_pr() is
effectively a no-op. But I guess REC_ENTER_EMULATED_MMIO is our way of
signalling to the RMM that it should skip the instruction, so your
proposed patch below makes the code slightly clearer.
Thanks,
Steve
> 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
