Re: [RFC PATCH 6/7] riscv: kvm: add SBI FWFT support for SBI_FWFT_DOUBLE_TRAP_ENABLE

[Deepak Gupta]

On Fri, Apr 26, 2024 at 06:17:08PM -0700, 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@xxxxxxxxxxxx>
> > ---
> > 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.
>
> Probably you need a check here whether underlying FW supports handling double
> trap.
>
> Am I missing something here?

On this I am indeed missing that menvcfg.DTE has to be 1 for any less priv.
So, nevermind on this comment. Sorry about that.