[PATCH v4 10/15] x86/xen/msr: Remove calling native_{read,write}_msr{,_safe}() in pmu_msr_{read,write}()

["Xin Li (Intel)" <xin@xxxxxxxxx>]

hpa found that pmu_msr_write() is actually a completely pointless
function [1]: all it does is shuffle some arguments, then calls
pmu_msr_chk_emulated() and if it returns true AND the emulated flag
is clear then does *exactly the same thing* that the calling code
would have done if pmu_msr_write() itself had returned true.  And
pmu_msr_read() does the equivalent stupidity.

Remove the calls to native_{read,write}_msr{,_safe}() within
pmu_msr_{read,write}().  Instead reuse the existing calling code
that decides whether to call native_{read,write}_msr{,_safe}() based
on the return value from pmu_msr_{read,write}().  Consequently,
eliminate the need to pass an error pointer to pmu_msr_{read,write}().

While at it, refactor pmu_msr_write() to take the MSR value as a u64
argument, replacing the current dual u32 arguments, because the dual
u32 arguments were only used to call native_write_msr{,_safe}(), which
has now been removed.

[1]: 
https://lore.kernel.org/lkml/0ec48b84-d158-47c6-b14c-3563fd14bcc4@xxxxxxxxx/

Suggested-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Sign-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---

Change in v3:
*) Rename pmu_msr_{read,write}() to pmu_msr_{read,write}_emulated()
   (Dapeng Mi).
*) Fix a pmu_msr_read() callsite with wrong arguments (Dapeng Mi).
---
 arch/x86/xen/enlighten_pv.c |  8 ++++++--
 arch/x86/xen/pmu.c          | 27 ++++-----------------------
 arch/x86/xen/xen-ops.h      |  4 ++--
 3 files changed, 12 insertions(+), 27 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 846b5737d320..61e51a970f3c 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1090,7 +1090,7 @@ static u64 xen_do_read_msr(unsigned int msr, int *err)
 {
        u64 val = 0;    /* Avoid uninitialized value for safe variant. */
 
-       if (pmu_msr_read(msr, &val, err))
+       if (pmu_msr_read_emulated(msr, &val))
                return val;
 
        if (err)
@@ -1132,6 +1132,8 @@ static void set_seg(unsigned int which, unsigned int low, 
unsigned int high,
 static void xen_do_write_msr(unsigned int msr, unsigned int low,
                             unsigned int high, int *err)
 {
+       u64 val;
+
        switch (msr) {
        case MSR_FS_BASE:
                set_seg(SEGBASE_FS, low, high, err);
@@ -1158,7 +1160,9 @@ static void xen_do_write_msr(unsigned int msr, unsigned 
int low,
                break;
 
        default:
-               if (!pmu_msr_write(msr, low, high, err)) {
+               val = (u64)high << 32 | low;
+
+               if (!pmu_msr_write_emulated(msr, val)) {
                        if (err)
                                *err = native_write_msr_safe(msr, low, high);
                        else
diff --git a/arch/x86/xen/pmu.c b/arch/x86/xen/pmu.c
index 9c1682af620a..b6557f2d1a2e 100644
--- a/arch/x86/xen/pmu.c
+++ b/arch/x86/xen/pmu.c
@@ -313,37 +313,18 @@ static bool pmu_msr_chk_emulated(unsigned int msr, 
uint64_t *val, bool is_read,
        return true;
 }
 
-bool pmu_msr_read(unsigned int msr, uint64_t *val, int *err)
+bool pmu_msr_read_emulated(u32 msr, u64 *val)
 {
        bool emulated;
 
-       if (!pmu_msr_chk_emulated(msr, val, true, &emulated))
-               return false;
-
-       if (!emulated) {
-               *val = err ? native_read_msr_safe(msr, err)
-                          : native_read_msr(msr);
-       }
-
-       return true;
+       return pmu_msr_chk_emulated(msr, val, true, &emulated) && emulated;
 }
 
-bool pmu_msr_write(unsigned int msr, uint32_t low, uint32_t high, int *err)
+bool pmu_msr_write_emulated(u32 msr, u64 val)
 {
-       uint64_t val = ((uint64_t)high << 32) | low;
        bool emulated;
 
-       if (!pmu_msr_chk_emulated(msr, &val, false, &emulated))
-               return false;
-
-       if (!emulated) {
-               if (err)
-                       *err = native_write_msr_safe(msr, low, high);
-               else
-                       native_write_msr(msr, low, high);
-       }
-
-       return true;
+       return pmu_msr_chk_emulated(msr, &val, false, &emulated) && emulated;
 }
 
 static u64 xen_amd_read_pmc(int counter)
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 735f58780704..163e03e33089 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -274,8 +274,8 @@ void xen_pmu_finish(int cpu);
 static inline void xen_pmu_init(int cpu) {}
 static inline void xen_pmu_finish(int cpu) {}
 #endif
-bool pmu_msr_read(unsigned int msr, uint64_t *val, int *err);
-bool pmu_msr_write(unsigned int msr, uint32_t low, uint32_t high, int *err);
+bool pmu_msr_read_emulated(u32 msr, u64 *val);
+bool pmu_msr_write_emulated(u32 msr, u64 val);
 int pmu_apic_update(uint32_t reg);
 u64 xen_read_pmc(int counter);
 
-- 
2.49.0