[PATCH 01/58] KVM: VMX: Enable io bitmaps to avoid IO port 0x80 VMEXITs

Avi Kivity
2007-06-17T09:43:42Z

From: He, Qing <qing.he-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

This patch enables IO bitmaps control on vmx and unmask the 0x80 port to
avoid VMEXITs caused by accessing port 0x80. 0x80 is used as delays (see
include/asm/io.h), and handling VMEXITs on its access is unnecessary but
slows things down. This patch improves kernel build test at around
3%~5%.
Because every VM uses the same io bitmap, it is shared between
all VMs rather than a per-VM data structure.

Signed-off-by: Qing He <qing.he-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Signed-off-by: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
---
drivers/kvm/vmx.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++----
1 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index c1ac106..52bd5f0 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -34,6 +34,9 @@ MODULE_LICENSE("GPL");
static DEFINE_PER_CPU(struct vmcs *, vmxarea);
static DEFINE_PER_CPU(struct vmcs *, current_vmcs);

+static struct page *vmx_io_bitmap_a;
+static struct page *vmx_io_bitmap_b;
+
#ifdef CONFIG_X86_64
#define HOST_IS_64 1
#else
@@ -1129,8 +1132,8 @@ static int vmx_vcpu_setup(struct kvm_vcpu *vcpu)
vmcs_write32(GUEST_PENDING_DBG_EXCEPTIONS, 0);

/* I/O */
- vmcs_write64(IO_BITMAP_A, 0);
- vmcs_write64(IO_BITMAP_B, 0);
+ vmcs_write64(IO_BITMAP_A, page_to_phys(vmx_io_bitmap_a));
+ vmcs_write64(IO_BITMAP_B, page_to_phys(vmx_io_bitmap_b));

guest_write_tsc(0);

@@ -1150,7 +1153,7 @@ static int vmx_vcpu_setup(struct kvm_vcpu *vcpu)
CPU_BASED_HLT_EXITING /* 20.6.2 */
| CPU_BASED_CR8_LOAD_EXITING /* 20.6.2 */
| CPU_BASED_CR8_STORE_EXITING /* 20.6.2 */
- | CPU_BASED_UNCOND_IO_EXITING /* 20.6.2 */
+ | CPU_BASED_ACTIVATE_IO_BITMAP /* 20.6.2 */
| CPU_BASED_MOV_DR_EXITING
| CPU_BASED_USE_TSC_OFFSETING /* 21.3 */
);
@@ -2188,11 +2191,50 @@ static struct kvm_arch_ops vmx_arch_ops = {

static int __init vmx_init(void)
{
- return kvm_init_arch(&vmx_arch_ops, THIS_MODULE);
+ void *iova;
+ int r;
+
+ vmx_io_bitmap_a = alloc_page(GFP_KERNEL | __GFP_HIGHMEM);
+ if (!vmx_io_bitmap_a)
+ return -ENOMEM;
+
+ vmx_io_bitmap_b = alloc_page(GFP_KERNEL | __GFP_HIGHMEM);
+ if (!vmx_io_bitmap_b) {
+ r = -ENOMEM;
+ goto out;
+ }
+
+ /*
+ * Allow direct access to the PC debug port (it is often used for I/O
+ * delays, but the vmexits simply slow things down).
+ */
+ iova = kmap(vmx_io_bitmap_a);
+ memset(iova, 0xff, PAGE_SIZE);
+ clear_bit(0x80, iova);
+ kunmap(iova);
+
+ iova = kmap(vmx_io_bitmap_b);
+ memset(iova, 0xff, PAGE_SIZE);
+ kunmap(iova);
+
+ r = kvm_init_arch(&vmx_arch_ops, THIS_MODULE);
+ if (r)
+ goto out1;
+
+ return 0;
+
+out1:
+ __free_page(vmx_io_bitmap_b);
+out:
+ __free_page(vmx_io_bitmap_a);
+ return r;
}

static void __exit vmx_exit(void)
{
+ __free_page(vmx_io_bitmap_b);
+ __free_page(vmx_io_bitmap_a);
+
kvm_exit_arch();