linux-kernel - [PATCH v4 2/4] RISC-V: KVM: Add VM capability to allow userspace get GPA bits

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Date:   Fri, 24 Dec 2021 13:06:02 +0530
From:   Anup Patel <anup.patel@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Atish Patra <atishp@...shpatra.org>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alistair Francis <Alistair.Francis@....com>,
        Anup Patel <anup@...infault.org>, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Anup Patel <anup.patel@....com>,
        Atish Patra <atishp@...osinc.com>
Subject: [PATCH v4 2/4] RISC-V: KVM: Add VM capability to allow userspace get GPA bits

The number of GPA bits supported for a RISC-V Guest/VM is based on the
MMU mode used by the G-stage translation. The KVM RISC-V will detect and
use the best possible MMU mode for the G-stage in kvm_arch_init().

We add a generic VM capability KVM_CAP_VM_GPA_BITS which can be used by
the KVM userspace to get the number of GPA (guest physical address) bits
supported for a Guest/VM.

Signed-off-by: Anup Patel <anup.patel@....com>
Reviewed-and-tested-by: Atish Patra <atishp@...osinc.com>
---
 arch/riscv/include/asm/kvm_host.h | 1 +
 arch/riscv/kvm/mmu.c              | 5 +++++
 arch/riscv/kvm/vm.c               | 3 +++
 include/uapi/linux/kvm.h          | 1 +
 4 files changed, 10 insertions(+)

diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index 247b761c72fd..ac38696abedf 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -219,6 +219,7 @@ void kvm_riscv_stage2_free_pgd(struct kvm *kvm);
 void kvm_riscv_stage2_update_hgatp(struct kvm_vcpu *vcpu);
 void kvm_riscv_stage2_mode_detect(void);
 unsigned long kvm_riscv_stage2_mode(void);
+int kvm_riscv_stage2_gpa_bits(void);
 
 void kvm_riscv_stage2_vmid_detect(void);
 unsigned long kvm_riscv_stage2_vmid_bits(void);
diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index d0efdc2259dc..58a47c93e5f9 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -766,3 +766,8 @@ unsigned long kvm_riscv_stage2_mode(void)
 {
 	return stage2_mode >> HGATP_MODE_SHIFT;
 }
+
+int kvm_riscv_stage2_gpa_bits(void)
+{
+	return stage2_gpa_bits;
+}
diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
index fb18af34a4b5..1e12c19a7c6a 100644
--- a/arch/riscv/kvm/vm.c
+++ b/arch/riscv/kvm/vm.c
@@ -82,6 +82,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_NR_MEMSLOTS:
 		r = KVM_USER_MEM_SLOTS;
 		break;
+	case KVM_CAP_VM_GPA_BITS:
+		r = kvm_riscv_stage2_gpa_bits();
+		break;
 	default:
 		r = 0;
 		break;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 1daa45268de2..469f05d69c8d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1131,6 +1131,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
 #define KVM_CAP_ARM_MTE 205
 #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
+#define KVM_CAP_VM_GPA_BITS 207
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
-- 
2.25.1