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Date: Tue, 14 May 2024 11:43:15 +0200
From: Clément Léger <cleger@...osinc.com>
To: Deepak Gupta <debug@...osinc.com>
Cc: Conor Dooley <conor@...nel.org>, Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
<palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
Anup Patel <anup@...infault.org>, Atish Patra <atishp@...shpatra.org>,
linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
kvm-riscv@...ts.infradead.org, Ved Shanbhogue <ved@...osinc.com>
Subject: Re: [RFC PATCH 6/7] riscv: kvm: add SBI FWFT support for
SBI_FWFT_DOUBLE_TRAP_ENABLE
On 27/04/2024 03:17, Deepak Gupta wrote:
> On Thu, Apr 18, 2024 at 04:26:45PM +0200, Clément Léger wrote:
>> Add support in KVM SBI FWFT extension to allow VS-mode to request double
>> trap enabling. Double traps can then be generated by VS-mode, allowing
>> M-mode to redirect them to S-mode.
>>
>> Signed-off-by: Clément Léger <cleger@...osinc.com>
>> ---
>> arch/riscv/include/asm/csr.h | 1 +
>> arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h | 2 +-
>> arch/riscv/kvm/vcpu_sbi_fwft.c | 41 ++++++++++++++++++++++
>> 3 files changed, 43 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
>> index 905cdf894a57..ee1b73655bec 100644
>> --- a/arch/riscv/include/asm/csr.h
>> +++ b/arch/riscv/include/asm/csr.h
>> @@ -196,6 +196,7 @@
>> /* xENVCFG flags */
>> #define ENVCFG_STCE (_AC(1, ULL) << 63)
>> #define ENVCFG_PBMTE (_AC(1, ULL) << 62)
>> +#define ENVCFG_DTE (_AC(1, ULL) << 59)
>> #define ENVCFG_CBZE (_AC(1, UL) << 7)
>> #define ENVCFG_CBCFE (_AC(1, UL) << 6)
>> #define ENVCFG_CBIE_SHIFT 4
>> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>> b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>> index 7dc1b80c7e6c..a9e20d655126 100644
>> --- a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>> @@ -11,7 +11,7 @@
>>
>> #include <asm/sbi.h>
>>
>> -#define KVM_SBI_FWFT_FEATURE_COUNT 1
>> +#define KVM_SBI_FWFT_FEATURE_COUNT 2
>>
>> struct kvm_sbi_fwft_config;
>> struct kvm_vcpu;
>> diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c
>> b/arch/riscv/kvm/vcpu_sbi_fwft.c
>> index b9b7f8fa6d22..9e8e397eb02f 100644
>> --- a/arch/riscv/kvm/vcpu_sbi_fwft.c
>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>> @@ -9,10 +9,19 @@
>> #include <linux/errno.h>
>> #include <linux/err.h>
>> #include <linux/kvm_host.h>
>> +#include <linux/riscv_dbltrp.h>
>> #include <asm/sbi.h>
>> #include <asm/kvm_vcpu_sbi.h>
>> #include <asm/kvm_vcpu_sbi_fwft.h>
>>
>> +#ifdef CONFIG_32BIT
>> +# define CSR_HENVCFG_DBLTRP CSR_HENVCFGH
>> +# define DBLTRP_DTE (ENVCFG_DTE >> 32)
>> +#else
>> +# define CSR_HENVCFG_DBLTRP CSR_HENVCFG
>> +# define DBLTRP_DTE ENVCFG_DTE
>> +#endif
>> +
>> #define MIS_DELEG (1UL << EXC_LOAD_MISALIGNED | 1UL <<
>> EXC_STORE_MISALIGNED)
>>
>> static int kvm_sbi_fwft_set_misaligned_delegation(struct kvm_vcpu *vcpu,
>> @@ -36,6 +45,33 @@ static int
>> kvm_sbi_fwft_get_misaligned_delegation(struct kvm_vcpu *vcpu,
>> return SBI_SUCCESS;
>> }
>>
>> +static int kvm_sbi_fwft_set_double_trap(struct kvm_vcpu *vcpu,
>> + struct kvm_sbi_fwft_config *conf,
>> + unsigned long value)
>> +{
>> + if (!riscv_double_trap_enabled())
>> + return SBI_ERR_NOT_SUPPORTED;
>
> Why its required to check whether host has enabled double trap for itself ?
> It's orthogonal to guest asking hypervisor to enable double trap.
Hi Deepak,
Indeed, as you saw, henvcfg.DTE needs menvcfg.DTE to be enabled in order
to be usable.
>
> Probably you need a check here whether underlying FW supports handling
> double
> trap.
>
> Am I missing something here?
>
>> +
>> + if (value)
>> + csr_set(CSR_HENVCFG_DBLTRP, DBLTRP_DTE);
>> + else
>> + csr_clear(CSR_HENVCFG_DBLTRP, DBLTRP_DTE);
>
> I think vcpu->arch.cfg has `henvcfg` field. Can we reflect it there as
> well so that current
> `henvcfg` copy in vcpu arch specifci config is consistent? Otherwise
> it'll be lost when vCPU
> is scheduled out and later scheduled back in (on vcpu load)
henvcfg is restored when loading the vpcu (kvm_arch_vcpu_load()) and
saved when the CPU is put (kvm_arch_vcpu_put()). But I just saw that
this change is included in the next patch. Should have been this one ,
I'll fix that.
>
> Furthermore, lets not do feature specific alias names for CSR.
>
> Instead let's keep consistent 64bit image of henvcfg in vcpu->arch.cfg.
>
> And whenever it's time to pick up the setting, pick up logic either
> perform the writes in
> henvcfg. And if required it'll perform henvcfgh too (as
> `kvm_arch_vcpu_load` already does)
I don't have a strong opinion on that point so if you think it really is
better, I'll switch to that.
Thanks,
Clément
>
>> +
>> + return SBI_SUCCESS;
>> +}
>> +
>> +static int kvm_sbi_fwft_get_double_trap(struct kvm_vcpu *vcpu,
>> + struct kvm_sbi_fwft_config *conf,
>> + unsigned long *value)
>> +{
>> + if (!riscv_double_trap_enabled())
>> + return SBI_ERR_NOT_SUPPORTED;
>> +
>> + *value = (csr_read(CSR_HENVCFG_DBLTRP) & DBLTRP_DTE) != 0;
>> +
>> + return SBI_SUCCESS;
>> +}
>> +
>> static struct kvm_sbi_fwft_config *
>> kvm_sbi_fwft_get_config(struct kvm_vcpu *vcpu, enum sbi_fwft_feature_t
>> feature)
>> {
>> @@ -111,6 +147,11 @@ static const struct kvm_sbi_fwft_feature
>> features[] = {
>> .id = SBI_FWFT_MISALIGNED_DELEG,
>> .set = kvm_sbi_fwft_set_misaligned_delegation,
>> .get = kvm_sbi_fwft_get_misaligned_delegation,
>> + },
>> + {
>> + .id = SBI_FWFT_DOUBLE_TRAP_ENABLE,
>> + .set = kvm_sbi_fwft_set_double_trap,
>> + .get = kvm_sbi_fwft_get_double_trap,
>> }
>> };
>>
>> --
>> 2.43.0
>>
>>
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