[Xen-devel] [PATCH v2 6/9] x86/vmx: Pass an MSR value into vmx_msr_add()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The main purpose of this change is to allow us to set a specific MSR value,
without needing to know whether there is already a load/save list slot for it.

Previously, callers wanting this property needed to call both vmx_add_*_msr()
and vmx_write_*_msr() to cover both cases, and there are no callers which want
the old behaviour of being a no-op if an entry already existed for the MSR.

As a result of this API improvement, the default value for guest MSRs need not
be 0, and the default for host MSRs need not be passed via hardware register.
In practice, this cleans up the VPMU allocation logic, and avoids an MSR read
as part of vcpu construction.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>

v2:
 * Document vmx_add_msr()'s behaviour.
 * Update commit message to indicate that noone wants the old behaviour.
---
 xen/arch/x86/cpu/vpmu_intel.c      |  6 ++----
 xen/arch/x86/hvm/vmx/vmcs.c        | 14 +++++++-------
 xen/arch/x86/hvm/vmx/vmx.c         |  2 +-
 xen/include/asm-x86/hvm/vmx/vmcs.h | 20 ++++++++++++++------
 4 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/xen/arch/x86/cpu/vpmu_intel.c b/xen/arch/x86/cpu/vpmu_intel.c
index c499e69..1fc79c9 100644
--- a/xen/arch/x86/cpu/vpmu_intel.c
+++ b/xen/arch/x86/cpu/vpmu_intel.c
@@ -454,13 +454,11 @@ static int core2_vpmu_alloc_resource(struct vcpu *v)
 
     if ( is_hvm_vcpu(v) )
     {
-        wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0);
-        if ( vmx_add_host_load_msr(v, MSR_CORE_PERF_GLOBAL_CTRL) )
+        if ( vmx_add_host_load_msr(v, MSR_CORE_PERF_GLOBAL_CTRL, 0) )
             goto out_err;
 
-        if ( vmx_add_guest_msr(v, MSR_CORE_PERF_GLOBAL_CTRL) )
+        if ( vmx_add_guest_msr(v, MSR_CORE_PERF_GLOBAL_CTRL, 0) )
             goto out_err;
-        vmx_write_guest_msr(v, MSR_CORE_PERF_GLOBAL_CTRL, 0);
     }
 
     core2_vpmu_cxt = xzalloc_bytes(sizeof(*core2_vpmu_cxt) +
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 2541ee0..c43b578 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1329,7 +1329,8 @@ struct vmx_msr_entry *vmx_find_msr(const struct vcpu *v, 
uint32_t msr,
     return ((ent < end) && (ent->index == msr)) ? ent : NULL;
 }
 
-int vmx_add_msr(struct vcpu *v, uint32_t msr, enum vmx_msr_list_type type)
+int vmx_add_msr(struct vcpu *v, uint32_t msr, uint64_t val,
+                enum vmx_msr_list_type type)
 {
     struct arch_vmx_struct *vmx = &v->arch.hvm_vmx;
     struct vmx_msr_entry **ptr, *start = NULL, *ent, *end;
@@ -1388,11 +1389,9 @@ int vmx_add_msr(struct vcpu *v, uint32_t msr, enum 
vmx_msr_list_type type)
     ent   = locate_msr_entry(start, end, msr);
 
     if ( (ent < end) && (ent->index == msr) )
-    {
-        rc = 0;
-        goto out;
-    }
+        goto found;
 
+    /* If there isn't an existing entry for msr, insert room for one. */
     if ( total == (PAGE_SIZE / sizeof(*ent)) )
     {
         rc = -ENOSPC;
@@ -1407,17 +1406,18 @@ int vmx_add_msr(struct vcpu *v, uint32_t msr, enum 
vmx_msr_list_type type)
     switch ( type )
     {
     case VMX_MSR_HOST:
-        rdmsrl(msr, ent->data);
         __vmwrite(VM_EXIT_MSR_LOAD_COUNT, ++vmx->host_msr_count);
         break;
 
     case VMX_MSR_GUEST:
-        ent->data = 0;
         __vmwrite(VM_EXIT_MSR_STORE_COUNT, ++vmx->msr_count);
         __vmwrite(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_count);
         break;
     }
 
+    /* Set the msr's value. */
+ found:
+    ent->data = val;
     rc = 0;
 
  out:
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 35f0e90..5ca0658 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -3103,7 +3103,7 @@ static int vmx_msr_write_intercept(unsigned int msr, 
uint64_t msr_content)
 
             for ( ; (rc == 0) && lbr->count; lbr++ )
                 for ( i = 0; (rc == 0) && (i < lbr->count); i++ )
-                    if ( (rc = vmx_add_guest_msr(v, lbr->base + i)) == 0 )
+                    if ( (rc = vmx_add_guest_msr(v, lbr->base + i, 0)) == 0 )
                         vmx_clear_msr_intercept(v, lbr->base + i, VMX_MSR_RW);
 
             v->arch.hvm_vmx.lbr_flags |= LBR_MSRS_INSERTED;
diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h 
b/xen/include/asm-x86/hvm/vmx/vmcs.h
index 37825ad..b4d23a1 100644
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -549,16 +549,24 @@ enum vmx_msr_list_type {
     VMX_MSR_GUEST,          /* MSRs saved on VMExit, loaded on VMEntry. */
 };
 
-int vmx_add_msr(struct vcpu *v, uint32_t msr, enum vmx_msr_list_type type);
+/**
+ * Add an MSR to an MSR list (inserting space for the entry if necessary), and
+ * set the MSRs value.
+ *
+ * May fail if unable to allocate memory for the list, or the total number of
+ * entries exceeds the memory allocated.
+ */
+int vmx_add_msr(struct vcpu *v, uint32_t msr, uint64_t val,
+                enum vmx_msr_list_type type);
 
-static inline int vmx_add_guest_msr(struct vcpu *v, uint32_t msr)
+static inline int vmx_add_guest_msr(struct vcpu *v, uint32_t msr, uint64_t val)
 {
-    return vmx_add_msr(v, msr, VMX_MSR_GUEST);
+    return vmx_add_msr(v, msr, val, VMX_MSR_GUEST);
 }
-
-static inline int vmx_add_host_load_msr(struct vcpu *v, uint32_t msr)
+static inline int vmx_add_host_load_msr(struct vcpu *v, uint32_t msr,
+                                        uint64_t val)
 {
-    return vmx_add_msr(v, msr, VMX_MSR_HOST);
+    return vmx_add_msr(v, msr, val, VMX_MSR_HOST);
 }
 
 struct vmx_msr_entry *vmx_find_msr(const struct vcpu *v, uint32_t msr,
-- 
2.1.4


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