Re: [PATCH v2] KVM: nVMX: Improve I/O exit handling

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2013-02-14 10:32, Gleb Natapov wrote:
> On Mon, Feb 11, 2013 at 12:19:17PM +0100, Jan Kiszka wrote:
>> This prevents trapping L2 I/O exits if L1 has neither unconditional nor
>> bitmap-based exiting enabled. Furthermore, it implements basic I/O
>> bitmap handling. Repeated string accesses are still reported to L1
>> unconditionally for now.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>
>> Changes in v2:
>>  - fix two brown-paper-bag bugs (offset for bitmap_b, wrong direction
>>    of mask shift)
>>  - use vmcs12 argument instead of get_vmcs12
>>
>>  arch/x86/kvm/vmx.c |   54 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 files changed, 52 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index fe9a9cf..64e1233 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -5913,6 +5913,57 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
>>  static const int kvm_vmx_max_exit_handlers =
>>  	ARRAY_SIZE(kvm_vmx_exit_handlers);
>>  
>> +static bool nested_vmx_exit_handled_io(struct kvm_vcpu *vcpu,
>> +				       struct vmcs12 *vmcs12)
>> +{
>> +	unsigned long exit_qualification;
>> +	gpa_t bitmap, last_bitmap;
>> +	bool string, rep;
>> +	u16 port;
>> +	int size;
>> +	u8 b;
>> +
>> +	if (nested_cpu_has(vmcs12, CPU_BASED_UNCOND_IO_EXITING))
>> +		return 1;
>> +
>> +	if (!nested_cpu_has(vmcs12, CPU_BASED_USE_IO_BITMAPS))
>> +		return 0;
>> +
>> +	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
>> +
>> +	string = exit_qualification & 16;
>> +	rep = exit_qualification & 32;
>> +
>> +	/* TODO: interpret instruction and check range against bitmap */
>> +	if (string && rep)
>> +		return 1;
>> +
>> +	port = exit_qualification >> 16;
>> +	size = (exit_qualification & 7) + 1;
>> +
>> +	last_bitmap = (gpa_t)-1;
>> +	b = -1;
>> +
>> +	while (size > 0) {
>> +		if (port < 0x8000)
>> +			bitmap = vmcs12->io_bitmap_a;
>> +		else
>> +			bitmap = vmcs12->io_bitmap_b;
>> +		bitmap += (port & 0x7fff) / 8;
>> +
>> +		if (last_bitmap != bitmap)
>> +			kvm_read_guest(vcpu->kvm, bitmap, &b, 1);
> Return value is ignored.

Not sure how to map a failure on real HW behaviour. I guess it's best to
simply initialize b to -1 before each call, enforcing an exit on
unaccessible bitmaps.

BTW, nested_vmx_exit_handled_msr needs some improvement in this regard, too.

Jan

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