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

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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.




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