An MSR value is represented as a 64-bit unsigned integer, with existing
MSR instructions storing it in EDX:EAX as two 32-bit segments.
The new immediate form MSR instructions, however, utilize a 64-bit
general-purpose register to store the MSR value. To unify the usage of
all MSR instructions, let the default MSR access APIs accept an MSR
value as a single 64-bit argument instead of two 32-bit segments.
The dual 32-bit APIs are still available as convenient wrappers over the
APIs that handle an MSR value as a single 64-bit argument.
The following illustrates the updated derivation of the MSR write APIs:
__wrmsrq(u32 msr, u64 val)
/ \
/ \
native_wrmsrq(msr, val) native_wrmsr(msr, low, high)
|
|
native_write_msr(msr, val)
/ \
/ \
wrmsrq(msr, val) wrmsr(msr, low, high)
When CONFIG_PARAVIRT is enabled, wrmsrq() and wrmsr() are defined on top
of paravirt_write_msr():
paravirt_write_msr(u32 msr, u64 val)
/ \
/ \
wrmsrq(msr, val) wrmsr(msr, low, high)
paravirt_write_msr() invokes cpu.write_msr(msr, val), an indirect layer
of pv_ops MSR write call:
If on native:
cpu.write_msr = native_write_msr
If on Xen:
cpu.write_msr = xen_write_msr
Therefore, refactor pv_cpu_ops.write_msr{_safe}() to accept an MSR value
in a single u64 argument, replacing the current dual u32 arguments.
No functional change intended.
Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
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