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-rw-r--r--Documentation/virt/kvm/api.txt9
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
index ebb37b34dcfc..3a0c819c3573 100644
--- a/Documentation/virt/kvm/api.txt
+++ b/Documentation/virt/kvm/api.txt
@@ -2196,6 +2196,15 @@ arm64 CCSIDR registers are demultiplexed by CSSELR value:
arm64 system registers have the following id bit patterns:
0x6030 0000 0013 <op0:2> <op1:3> <crn:4> <crm:4> <op2:3>
+WARNING:
+ Two system register IDs do not follow the specified pattern. These
+ are KVM_REG_ARM_TIMER_CVAL and KVM_REG_ARM_TIMER_CNT, which map to
+ system registers CNTV_CVAL_EL0 and CNTVCT_EL0 respectively. These
+ two had their values accidentally swapped, which means TIMER_CVAL is
+ derived from the register encoding for CNTVCT_EL0 and TIMER_CNT is
+ derived from the register encoding for CNTV_CVAL_EL0. As this is
+ API, it must remain this way.
+
arm64 firmware pseudo-registers have the following bit pattern:
0x6030 0000 0014 <regno:16>