linux-kernel - Re: [PATCH v2 4/8] RISC-V: KVM: Forward SBI DBCN extension to user-space

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Message-ID: <20231019-7471d3927d94ab7158d61c6b@orel>
Date:   Thu, 19 Oct 2023 11:17:26 +0200
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Anup Patel <apatel@...tanamicro.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Atish Patra <atishp@...shpatra.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Conor Dooley <conor@...nel.org>, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-serial@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/8] RISC-V: KVM: Forward SBI DBCN extension to
 user-space

On Thu, Oct 12, 2023 at 10:45:05AM +0530, Anup Patel wrote:
> The frozen SBI v2.0 specification defines the SBI debug console
> (DBCN) extension which replaces the legacy SBI v0.1 console
> functions namely sbi_console_getchar() and sbi_console_putchar().
> 
> The SBI DBCN extension needs to be emulated in the KVM user-space
> (i.e. QEMU-KVM or KVMTOOL) so we forward SBI DBCN calls from KVM
> guest to the KVM user-space which can then redirect the console
> input/output to wherever it wants (e.g. telnet, file, stdio, etc).
> 
> The SBI debug console is simply a early console available to KVM
> guest for early prints and it does not intend to replace the proper
> console devices such as 8250, VirtIO console, etc.
> 
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> ---
>  arch/riscv/include/asm/kvm_vcpu_sbi.h |  1 +
>  arch/riscv/include/uapi/asm/kvm.h     |  1 +
>  arch/riscv/kvm/vcpu_sbi.c             |  4 ++++
>  arch/riscv/kvm/vcpu_sbi_replace.c     | 32 +++++++++++++++++++++++++++
>  4 files changed, 38 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> index c02bda5559d7..6a453f7f8b56 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> @@ -73,6 +73,7 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_ipi;
>  extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_rfence;
>  extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_srst;
>  extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm;
> +extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbcn;
>  extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_experimental;
>  extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_vendor;
>  
> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index 917d8cc2489e..60d3b21dead7 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -156,6 +156,7 @@ enum KVM_RISCV_SBI_EXT_ID {
>  	KVM_RISCV_SBI_EXT_PMU,
>  	KVM_RISCV_SBI_EXT_EXPERIMENTAL,
>  	KVM_RISCV_SBI_EXT_VENDOR,
> +	KVM_RISCV_SBI_EXT_DBCN,

We should add this new register to the get-reg-list kselftest, i.e.

diff --git a/tools/testing/selftests/kvm/riscv/get-reg-list.c b/tools/testing/selftests/kvm/riscv/get-reg-list.c
index 234006d035c9..4a0f8a8cfbf8 100644
--- a/tools/testing/selftests/kvm/riscv/get-reg-list.c
+++ b/tools/testing/selftests/kvm/riscv/get-reg-list.c
@@ -565,6 +565,7 @@ static __u64 base_regs[] = {
 	KVM_REG_RISCV | KVM_REG_SIZE_ULONG | KVM_REG_RISCV_SBI_EXT | KVM_REG_RISCV_SBI_SINGLE | KVM_RISCV_SBI_EXT_SRST,
 	KVM_REG_RISCV | KVM_REG_SIZE_ULONG | KVM_REG_RISCV_SBI_EXT | KVM_REG_RISCV_SBI_SINGLE | KVM_RISCV_SBI_EXT_HSM,
 	KVM_REG_RISCV | KVM_REG_SIZE_ULONG | KVM_REG_RISCV_SBI_EXT | KVM_REG_RISCV_SBI_SINGLE | KVM_RISCV_SBI_EXT_PMU,
+	KVM_REG_RISCV | KVM_REG_SIZE_ULONG | KVM_REG_RISCV_SBI_EXT | KVM_REG_RISCV_SBI_SINGLE | KVM_RISCV_SBI_EXT_DBCN,
 	KVM_REG_RISCV | KVM_REG_SIZE_ULONG | KVM_REG_RISCV_SBI_EXT | KVM_REG_RISCV_SBI_SINGLE | KVM_RISCV_SBI_EXT_EXPERIMENTAL,
 	KVM_REG_RISCV | KVM_REG_SIZE_ULONG | KVM_REG_RISCV_SBI_EXT | KVM_REG_RISCV_SBI_SINGLE | KVM_RISCV_SBI_EXT_VENDOR,
 	KVM_REG_RISCV | KVM_REG_SIZE_ULONG | KVM_REG_RISCV_SBI_EXT | KVM_REG_RISCV_SBI_MULTI_EN | 0,

Thanks,
drew