Commit fdef3ad1 authored by He, Qing's avatar He, Qing Committed by Avi Kivity
Browse files

KVM: VMX: Enable io bitmaps to avoid IO port 0x80 VMEXITs 



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: default avatarQing He <qing.he@intel.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 8f41958b

drivers/kvm/vmx.c

+46 −4
Original line number Diff line number Diff line
@@ -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();

}

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