Re: [PATCH v5] KVM: nVMX: Improve I/O exit handling

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-02-18 10:36, Gleb Natapov wrote:
> On Mon, Feb 18, 2013 at 10:17:14AM +0100, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> This prevents trapping L2 I/O exits if L1 has neither unconditional nor
>> bitmap-based exiting enabled. Furthermore, it implements I/O bitmap
>> handling. We still exit unconditionally in case the CPU does not provide
>> information for ins/outs.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>
>> Changes in v5:
>>  - still exit unconditionally if CPU refuses to provide exit
>>    information on ins/outs
>>
>>  arch/x86/kvm/vmx.c |   58 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 files changed, 56 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 6667042..ccc7c17 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -651,6 +651,7 @@ static struct vmcs_config {
>>  	int size;
>>  	int order;
>>  	u32 revision_id;
>> +	u32 vmx_basic_high;
>>  	u32 pin_based_exec_ctrl;
>>  	u32 cpu_based_exec_ctrl;
>>  	u32 cpu_based_2nd_exec_ctrl;
>> @@ -752,6 +753,11 @@ static inline bool vm_need_tpr_shadow(struct kvm *kvm)
>>  	return (cpu_has_vmx_tpr_shadow()) && (irqchip_in_kernel(kvm));
>>  }
>>  
>> +static inline bool cpu_has_stringio_exit_info(void)
>> +{
>> +	return vmcs_config.vmx_basic_high & (VMX_BASIC_INOUT >> 32);
>> +}
>> +
>>  static inline bool cpu_has_secondary_exec_ctrls(void)
>>  {
>>  	return vmcs_config.cpu_based_exec_ctrl &
>> @@ -2635,6 +2641,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
>>  	vmcs_conf->size = vmx_msr_high & 0x1fff;
>>  	vmcs_conf->order = get_order(vmcs_config.size);
>>  	vmcs_conf->revision_id = vmx_msr_low;
>> +	vmcs_conf->vmx_basic_high = vmx_msr_high;
>>  
>>  	vmcs_conf->pin_based_exec_ctrl = _pin_based_exec_control;
>>  	vmcs_conf->cpu_based_exec_ctrl = _cpu_based_exec_control;
>> @@ -5908,6 +5915,54 @@ 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;
>> +	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;
>> +
>> +	/* TODO: for older CPUs, derive access width from instruction */
>> +	if (!cpu_has_stringio_exit_info())
>> +		return 1;
>> +
> 
> Sigh, actually I am stupid :( The information that is not available
> on older cpus is address size in "VM-exit instruction information",
> not operand size on exit qualification, so your v4 is correct. Except
> handling of port wrap around:
> 
>   If the “use I/O bitmaps” VM-execution control is 1, the instruction
>   causes a VM exit if it attempts to access an I/O port corresponding to a
>   bit set to 1 in the appropriate I/O bitmap (see Section 24.6.4). If an
>   I/O operation “wraps around” the 16-bit I/O-port space (accesses
>   ports FFFFH and 0000H), the I/O instruction causes a VM exit (the
>   “unconditional I/O exiting” VM-execution control is ignored if the
>   “use I/O bitmaps” VM-execution control is 1).

Ah, indeed.

OK, let's see if this "simple" patch manages to reach two-digit revision
numbers...

Jan



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