On 02/25/2010 07:15 PM, Joerg Roedel wrote:
This patch optimizes the way the msrpm of the host and the
guest are merged. The old code merged the 2 msrpm pages
completly. This code needed to touch 24kb of memory for that
operation. The optimized variant this patch introduces
merges only the parts where the host msrpm may contain zero
bits. This reduces the amount of memory which is touched to
48 bytes.
Signed-off-by: Joerg Roedel<joerg.roedel@xxxxxxx>
---
arch/x86/kvm/svm.c | 67 +++++++++++++++++++++++++++++++++++++++++++++-------
1 files changed, 58 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d8d4e35..d15e0ea 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -92,6 +92,9 @@ struct nested_state {
};
+#define MSRPM_OFFSETS 16
+static u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
+
struct vcpu_svm {
struct kvm_vcpu vcpu;
struct vmcb *vmcb;
@@ -436,6 +439,34 @@ err_1:
}
+static void add_msr_offset(u32 offset)
+{
+ u32 old;
+ int i;
+
+again:
+ for (i = 0; i< MSRPM_OFFSETS; ++i) {
+ old = msrpm_offsets[i];
+
+ if (old == offset)
+ return;
+
+ if (old != MSR_INVALID)
+ continue;
+
+ if (cmpxchg(&msrpm_offsets[i], old, offset) != old)
+ goto again;
+
+ return;
+ }
+
+ /*
+ * If this BUG triggers the msrpm_offsets table has an overflow. Just
+ * increase MSRPM_OFFSETS in this case.
+ */
+ BUG();
+}
Why all this atomic cleverness? The possible offsets are all determined
statically. Even if you do them dynamically (makes sense when
considering pmu passthrough), it's per-vcpu and therefore single
threaded (just move msrpm_offsets into vcpu context).
@@ -1846,20 +1882,33 @@ static int nested_svm_vmexit(struct vcpu_svm *svm)
static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
{
- u32 *nested_msrpm;
- struct page *page;
+ /*
+ * This function merges the msr permission bitmaps of kvm and the
+ * nested vmcb. It is omptimized in that it only merges the parts where
+ * the kvm msr permission bitmap may contain zero bits
+ */
A comment that describes the entire function can be moved above the
function, freeing a whole tab stop for contents.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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