linux-kernel - Re: [PATCH v8 34/43] arm64: RME: Propagate number of breakpoints and watchpoints to userspace

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Message-ID: <cfa0ba0f-86ad-4a72-be14-67b0639a7f59@redhat.com>
Date: Thu, 1 May 2025 13:40:01 +1000
From: Gavin Shan <gshan@...hat.com>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>,
 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>,
 Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun
 <alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v8 34/43] arm64: RME: Propagate number of breakpoints and
 watchpoints to userspace

On 5/1/25 1:36 PM, Gavin Shan wrote:
> On 4/16/25 11:41 PM, Steven Price wrote:
>> From: Jean-Philippe Brucker <jean-philippe@...aro.org>
>>
>> The RMM describes the maximum number of BPs/WPs available to the guest
>> in the Feature Register 0. Propagate those numbers into ID_AA64DFR0_EL1,
>> which is visible to userspace. A VMM needs this information in order to
>> set up realm parameters.
>>
>> Signed-off-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
>> Signed-off-by: Steven Price <steven.price@....com>
>> ---
>>   arch/arm64/include/asm/kvm_rme.h |  2 ++
>>   arch/arm64/kvm/rme.c             | 22 ++++++++++++++++++++++
>>   arch/arm64/kvm/sys_regs.c        |  2 +-
>>   3 files changed, 25 insertions(+), 1 deletion(-)
>>
> 
> If I don't miss anything, it's not enough to apply the filter on reading and
> resetting path where sanitise_id_aa64dfr0_el1() is called. id_aa64dfr0_el1
> is writable and it's possible that QEMU modifies its value. Afterwards, the
> register is read from guest kernel, which will be trapped to host and the
> modified value is returned, without this filter applied. So I think the same
> filter need to be applied to the write path originated from QEMU.
> 

Please ignore this and it has been done in next patch :)

Thanks,
Gavin

>> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
>> index f786fd978cf6..09cbb61816f3 100644
>> --- a/arch/arm64/include/asm/kvm_rme.h
>> +++ b/arch/arm64/include/asm/kvm_rme.h
>> @@ -94,6 +94,8 @@ void kvm_init_rme(void);
>>   u32 kvm_realm_ipa_limit(void);
>>   u32 kvm_realm_vgic_nr_lr(void);
>> +u64 kvm_realm_reset_id_aa64dfr0_el1(const struct kvm_vcpu *vcpu, u64 val);
>> +
>>   bool kvm_rme_supports_sve(void);
>>   int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
>> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
>> index 297b13ef1729..0c358ce0a7a1 100644
>> --- a/arch/arm64/kvm/rme.c
>> +++ b/arch/arm64/kvm/rme.c
>> @@ -87,6 +87,28 @@ u32 kvm_realm_vgic_nr_lr(void)
>>       return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_GICV3_NUM_LRS);
>>   }
>> +u64 kvm_realm_reset_id_aa64dfr0_el1(const struct kvm_vcpu *vcpu, u64 val)
>> +{
>> +    u32 bps = u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_NUM_BPS);
>> +    u32 wps = u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_NUM_WPS);
>> +    u32 ctx_cmps;
>> +
>> +    if (!kvm_is_realm(vcpu->kvm))
>> +        return val;
>> +
>> +    /* Ensure CTX_CMPs is still valid */
>> +    ctx_cmps = FIELD_GET(ID_AA64DFR0_EL1_CTX_CMPs, val);
>> +    ctx_cmps = min(bps, ctx_cmps);
>> +
>> +    val &= ~(ID_AA64DFR0_EL1_BRPs_MASK | ID_AA64DFR0_EL1_WRPs_MASK |
>> +         ID_AA64DFR0_EL1_CTX_CMPs);
>> +    val |= FIELD_PREP(ID_AA64DFR0_EL1_BRPs_MASK, bps) |
>> +           FIELD_PREP(ID_AA64DFR0_EL1_WRPs_MASK, wps) |
>> +           FIELD_PREP(ID_AA64DFR0_EL1_CTX_CMPs, ctx_cmps);
>> +
>> +    return val;
>> +}
>> +
>>   static int get_start_level(struct realm *realm)
>>   {
>>       return 4 - ((realm->ia_bits - 8) / (RMM_PAGE_SHIFT - 3));
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index de7fe024dbff..36e22ed84e7e 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -1844,7 +1844,7 @@ static u64 sanitise_id_aa64dfr0_el1(const struct kvm_vcpu *vcpu, u64 val)
>>       /* Hide BRBE from guests */
>>       val &= ~ID_AA64DFR0_EL1_BRBE_MASK;
>> -    return val;
>> +    return kvm_realm_reset_id_aa64dfr0_el1(vcpu, val);
>>   }
>>   static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
>