[PATCH v5 09/27] KVM: arm64: Make ID_AA64MMFR1_EL1 writable

[Reiji Watanabe]

This patch adds id_reg_info for ID_AA64MMFR1_EL1 to make it
writable by userspace.

Hardware update of Access flag and/or Dirty state in translation
table needs to be disabled for the guest to let userspace set
ID_AA64MMFR1_EL1.HAFDBS field to a lower value. It requires trapping
the guest's accessing TCR_EL1, which KVM doesn't always do (in order
to trap it without FEAT_FGT, HCR_EL2.TVM needs to be set to 1, which
also traps many other virtual memory control registers).
So, userspace won't be allowed to modify the value of the HAFDBS field.

Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/kvm/sys_regs.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 4ed15ae7f160..1c137f8c236f 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -570,6 +570,30 @@ static int validate_id_aa64mmfr0_el1(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+static int validate_id_aa64mmfr1_el1(struct kvm_vcpu *vcpu,
+				     const struct id_reg_info *id_reg, u64 val)
+{
+	u64 limit = id_reg->vcpu_limit_val;
+	unsigned int hafdbs, lim_hafdbs;
+
+	hafdbs = cpuid_feature_extract_unsigned_field(val, ID_AA64MMFR1_HADBS_SHIFT);
+	lim_hafdbs = cpuid_feature_extract_unsigned_field(limit, ID_AA64MMFR1_HADBS_SHIFT);
+
+	/*
+	 * Don't allow userspace to modify the value of HAFDBS.
+	 * Hardware update of Access flag and/or Dirty state in translation
+	 * table needs to be disabled for the guest to let userspace set
+	 * HAFDBS field to a lower value. It requires trapping the guest's
+	 * accessing TCR_EL1, which KVM doesn't always do (in order to trap
+	 * it without FEAT_FGT, HCR_EL2.TVM needs to be set to 1, which also
+	 * traps many other virtual memory control registers).
+	 */
+	if (hafdbs != lim_hafdbs)
+		return -EINVAL;
+
+	return 0;
+}
+
 static void init_id_aa64pfr0_el1_info(struct id_reg_info *id_reg)
 {
 	u64 limit = id_reg->vcpu_limit_val;
@@ -675,6 +699,11 @@ static struct id_reg_info id_aa64mmfr0_el1_info = {
 	.validate = validate_id_aa64mmfr0_el1,
 };
 
+static struct id_reg_info id_aa64mmfr1_el1_info = {
+	.sys_reg = SYS_ID_AA64MMFR1_EL1,
+	.validate = validate_id_aa64mmfr1_el1,
+};
+
 /*
  * An ID register that needs special handling to control the value for the
  * guest must have its own id_reg_info in id_reg_info_table.
@@ -689,6 +718,7 @@ static struct id_reg_info *id_reg_info_table[KVM_ARM_ID_REG_MAX_NUM] = {
 	[IDREG_IDX(SYS_ID_AA64ISAR0_EL1)] = &id_aa64isar0_el1_info,
 	[IDREG_IDX(SYS_ID_AA64ISAR1_EL1)] = &id_aa64isar1_el1_info,
 	[IDREG_IDX(SYS_ID_AA64MMFR0_EL1)] = &id_aa64mmfr0_el1_info,
+	[IDREG_IDX(SYS_ID_AA64MMFR1_EL1)] = &id_aa64mmfr1_el1_info,
 };
 
 static int validate_id_reg(struct kvm_vcpu *vcpu, u32 id, u64 val)
-- 
2.35.1.265.g69c8d7142f-goog