x86/pvops/msr: Refactor pv_cpu_ops.write_msr{,_safe}()

x86/pvops/msr: Refactor pv_cpu_ops.write_msr{,_safe}()

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@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20250427092027.1598740-14-xin@zytor.com