[RFC PATCH 08/14] RISC-V: KVM: Implement SBI STA extension

[Andrew Jones]

Add a select SCHED_INFO to the KVM config in order to get run_delay
info. Then implement SBI STA's set-steal-time-shmem function and
kvm_riscv_vcpu_record_steal_time() to provide the steal-time info
to guests.

Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
---
 arch/riscv/kvm/Kconfig        |  1 +
 arch/riscv/kvm/vcpu_sbi_sta.c | 96 ++++++++++++++++++++++++++++++++++-
 2 files changed, 95 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kvm/Kconfig b/arch/riscv/kvm/Kconfig
index 5bcb2d519b95..7decdec691af 100644
--- a/arch/riscv/kvm/Kconfig
+++ b/arch/riscv/kvm/Kconfig
@@ -28,6 +28,7 @@ config KVM
 	select KVM_XFER_TO_GUEST_WORK
 	select MMU_NOTIFIER
 	select PREEMPT_NOTIFIERS
+	select SCHED_INFO
 	select SRCU
 	help
 	  Support hosting virtualized guest machines.
diff --git a/arch/riscv/kvm/vcpu_sbi_sta.c b/arch/riscv/kvm/vcpu_sbi_sta.c
index ecf679082007..bc4f7390a9a8 100644
--- a/arch/riscv/kvm/vcpu_sbi_sta.c
+++ b/arch/riscv/kvm/vcpu_sbi_sta.c
@@ -3,22 +3,114 @@
  * Copyright (c) 2023 Ventana Micro Systems Inc.
  */
 
+#include <linux/kernel.h>
 #include <linux/kvm_host.h>
+#include <linux/mm.h>
+#include <linux/sizes.h>
 
+#include <asm/bug.h>
+#include <asm/current.h>
 #include <asm/kvm_vcpu_sbi.h>
+#include <asm/page.h>
 #include <asm/sbi.h>
+#include <asm/uaccess.h>
 
 void kvm_riscv_vcpu_record_steal_time(struct kvm_vcpu *vcpu)
 {
 	gpa_t shmem = vcpu->arch.sta.shmem;
+	u64 last_steal = vcpu->arch.sta.last_steal;
+	u32 *sequence_ptr, sequence;
+	u64 *steal_ptr, steal;
+	unsigned long hva;
+	gfn_t gfn;
 
 	if (shmem == INVALID_GPA)
 		return;
+
+	/*
+	 * shmem is 64-byte aligned (see the enforcement in
+	 * kvm_sbi_sta_set_steal_time_shmem()) and the size of sbi_sta_struct
+	 * is 64 bytes, so we know all its offsets are in the same page.
+	 */
+	gfn = shmem >> PAGE_SHIFT;
+	hva = kvm_vcpu_gfn_to_hva(vcpu, gfn);
+
+	if (WARN_ON(kvm_is_error_hva(hva))) {
+		vcpu->arch.sta.shmem = INVALID_GPA;
+		return;
+	}
+
+	sequence_ptr = (u32 *)(hva + offset_in_page(shmem) +
+			       offsetof(struct sbi_sta_struct, sequence));
+	steal_ptr = (u64 *)(hva + offset_in_page(shmem) +
+			    offsetof(struct sbi_sta_struct, steal));
+
+	if (WARN_ON(get_user(sequence, sequence_ptr)))
+		return;
+
+	sequence = le32_to_cpu(sequence);
+	sequence += 1;
+
+	if (WARN_ON(put_user(cpu_to_le32(sequence), sequence_ptr)))
+		return;
+
+	if (!WARN_ON(get_user(steal, steal_ptr))) {
+		steal = le64_to_cpu(steal);
+		vcpu->arch.sta.last_steal = READ_ONCE(current->sched_info.run_delay);
+		steal += vcpu->arch.sta.last_steal - last_steal;
+		WARN_ON(put_user(cpu_to_le64(steal), steal_ptr));
+	}
+
+	sequence += 1;
+	WARN_ON(put_user(cpu_to_le32(sequence), sequence_ptr));
+
+	kvm_vcpu_mark_page_dirty(vcpu, gfn);
 }
 
 static int kvm_sbi_sta_set_steal_time_shmem(struct kvm_vcpu *vcpu)
 {
-	return SBI_ERR_FAILURE;
+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	unsigned long shmem_phys_lo = cp->a0;
+	unsigned long shmem_phys_hi = cp->a1;
+	u32 flags = cp->a2;
+	struct sbi_sta_struct zero_sta = {0};
+	unsigned long hva;
+	bool writable;
+	gpa_t shmem;
+	int ret;
+
+	if (flags != 0)
+		return SBI_ERR_INVALID_PARAM;
+
+	if (shmem_phys_lo == -1 && shmem_phys_hi == -1) {
+		vcpu->arch.sta.shmem = INVALID_GPA;
+		return 0;
+	}
+
+	if (shmem_phys_lo & (SZ_64 - 1))
+		return SBI_ERR_INVALID_PARAM;
+
+	shmem = shmem_phys_lo;
+
+	if (shmem_phys_hi != 0)
+#ifdef CONFIG_32BIT
+		shmem |= ((gpa_t)shmem_phys_hi << 32);
+#else
+		return SBI_ERR_INVALID_ADDRESS;
+#endif
+
+	hva = kvm_vcpu_gfn_to_hva_prot(vcpu, shmem >> PAGE_SHIFT, &writable);
+	if (kvm_is_error_hva(hva) || !writable)
+		return SBI_ERR_INVALID_ADDRESS;
+
+	ret = kvm_vcpu_write_guest(vcpu, shmem, &zero_sta, sizeof(zero_sta));
+	if (ret)
+		return SBI_ERR_FAILURE;
+
+	vcpu->arch.sta.shmem = shmem;
+	vcpu->arch.sta.last_steal = current->sched_info.run_delay;
+
+	return 0;
 }
 
 static int kvm_sbi_ext_sta_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
@@ -44,7 +136,7 @@ static int kvm_sbi_ext_sta_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 
 static unsigned long kvm_sbi_ext_sta_probe(struct kvm_vcpu *vcpu)
 {
-	return 0;
+	return !!sched_info_on();
 }
 
 const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_sta = {
-- 
2.39.2