linux-kernel - Re: [RFC PATCH 6/7] riscv: kvm: add SBI FWFT support for SBI_FWFT_DOUBLE_TRAP

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Message-ID: <Zi0bZPoNIYbanIfO@debug.ba.rivosinc.com>
Date: Sat, 27 Apr 2024 08:36:04 -0700
From: Deepak Gupta <debug@...osinc.com>
To: Clément Léger <cleger@...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 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@...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.
>
>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.