[Xen-devel] [PATCH v2 8/9] x86/vmx: Support removing MSRs from the host/guest load/save lists

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Up until this point, the MSR load/save lists have only ever accumulated
content.  Introduce vmx_del_msr() as a companion to vmx_add_msr().

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:
 * s/arch_vmx/vmx/ as per patch 2 review
---
 xen/arch/x86/hvm/vmx/vmcs.c        | 68 ++++++++++++++++++++++++++++++++++++++
 xen/include/asm-x86/hvm/vmx/vmcs.h |  6 ++++
 2 files changed, 74 insertions(+)

diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 4fb3043..0ebccc4 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1452,6 +1452,74 @@ int vmx_add_msr(struct vcpu *v, uint32_t msr, uint64_t 
val,
     return rc;
 }
 
+int vmx_del_msr(struct vcpu *v, uint32_t msr, enum vmx_msr_list_type type)
+{
+    struct arch_vmx_struct *vmx = &v->arch.hvm_vmx;
+    struct vmx_msr_entry *start = NULL, *ent, *end;
+    unsigned int substart, subend, total;
+
+    ASSERT(v == current || !vcpu_runnable(v));
+
+    switch ( type )
+    {
+    case VMX_MSR_HOST:
+        start    = vmx->host_msr_area;
+        substart = 0;
+        subend   = vmx->host_msr_count;
+        total    = subend;
+        break;
+
+    case VMX_MSR_GUEST:
+        start    = vmx->msr_area;
+        substart = 0;
+        subend   = vmx->msr_save_count;
+        total    = vmx->msr_load_count;
+        break;
+
+    case VMX_MSR_GUEST_LOADONLY:
+        start    = vmx->msr_area;
+        substart = vmx->msr_save_count;
+        subend   = vmx->msr_load_count;
+        total    = subend;
+        break;
+
+    default:
+        ASSERT_UNREACHABLE();
+    }
+
+    if ( !start )
+        return -ESRCH;
+
+    end = start + total;
+    ent = locate_msr_entry(start + substart, start + subend, msr);
+
+    if ( (ent == end) || (ent->index != msr) )
+        return -ESRCH;
+
+    memmove(ent, ent + 1, sizeof(*ent) * (end - ent));
+
+    vmx_vmcs_enter(v);
+
+    switch ( type )
+    {
+    case VMX_MSR_HOST:
+        __vmwrite(VM_EXIT_MSR_LOAD_COUNT, vmx->host_msr_count--);
+        break;
+
+    case VMX_MSR_GUEST:
+        __vmwrite(VM_EXIT_MSR_STORE_COUNT, vmx->msr_save_count--);
+
+        /* Fallthrough */
+    case VMX_MSR_GUEST_LOADONLY:
+        __vmwrite(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_load_count--);
+        break;
+    }
+
+    vmx_vmcs_exit(v);
+
+    return 0;
+}
+
 void vmx_set_eoi_exit_bitmap(struct vcpu *v, u8 vector)
 {
     if ( !test_and_set_bit(vector, v->arch.hvm_vmx.eoi_exit_bitmap) )
diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h 
b/xen/include/asm-x86/hvm/vmx/vmcs.h
index 3764982..6629b4f 100644
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -564,6 +564,12 @@ enum vmx_msr_list_type {
 int vmx_add_msr(struct vcpu *v, uint32_t msr, uint64_t val,
                 enum vmx_msr_list_type type);
 
+/**
+ * Remove an MSR entry from an MSR list.  Returns -ESRCH if the MSR was not
+ * found in the list.
+ */
+int vmx_del_msr(struct vcpu *v, uint32_t msr, enum vmx_msr_list_type type);
+
 static inline int vmx_add_guest_msr(struct vcpu *v, uint32_t msr, uint64_t val)
 {
     return vmx_add_msr(v, msr, val, VMX_MSR_GUEST);
-- 
2.1.4


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