KVM chooses not to support MPX in the guest unless both of these control bits are supported by the platform. On Fri, Nov 3, 2017 at 10:13 AM, Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> wrote: > > > On 11/02/2017 11:40 PM, Wanpeng Li wrote: >> >> 2017-11-03 14:31 GMT+08:00 Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>: >>> >>> >>> On 11/02/2017 05:50 PM, Wanpeng Li wrote: >>>> >>>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>>> >>>> According to the SDM, if the "load IA32_BNDCFGS" VM-entry controls is 1, >>>> the >>>> following checks are performed on the field for the IA32_BNDCFGS MSR: >>>> - Bits reserved in the IA32_BNDCFGS MSR must be 0. >>>> - The linear address in bits 63:12 must be canonical. >>>> >>>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> >>>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> >>>> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> >>>> Cc: Jim Mattson <jmattson@xxxxxxxxxx> >>>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>>> --- >>>> v3 -> v4: >>>> * simply condition >>>> * use && instead of nested "if"s >>>> >>>> arch/x86/kvm/vmx.c | 5 +++++ >>>> 1 file changed, 5 insertions(+) >>>> >>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>>> index e6c8ffa..6cf3972 100644 >>>> --- a/arch/x86/kvm/vmx.c >>>> +++ b/arch/x86/kvm/vmx.c >>>> @@ -10805,6 +10805,11 @@ static int check_vmentry_postreqs(struct >>>> kvm_vcpu >>>> *vcpu, struct vmcs12 *vmcs12, >>>> return 1; >>>> } >>>> + if (kvm_mpx_supported() && >>>> + (is_noncanonical_address(vmcs12->guest_bndcfgs & >>>> PAGE_MASK, vcpu) || >>>> + (vmcs12->guest_bndcfgs & MSR_IA32_BNDCFGS_RSVD))) >>>> + return 1; >>>> + >>>> return 0; >>>> } >>>> >>> Hi Wanpeng, >>> The SDM check is performed only when "load IA32_BNDCFGS" VM-entry >>> control >>> is 1. But vmx_mpx_supported() returns true when both "load IA32_BNDCFGS" >>> and >>> "store IA32_BNDCFGS" VM-entry controls are 1. Therefore your check is >>> performed when both controls are 1. Did I miss something here ? >> >> https://lkml.org/lkml/2017/11/2/748 Paolo hopes the simplification. >> >> Regards, >> Wanpeng Li > > I got that simplification and your changes look good to me. > > > However, I am still curious know the reason why vmx_mpx_supported() returns > true only when both controls are true whereas the SDM states the following: > > "IA32_BNDCFGS (64 bits). This field is supported only on processors that > support either the 1-setting of the “load IA32_BNDCFGS” VM-entry control or > that of the “clear IA32_BNDCFGS” VM-exit control." > > Thanks, > Krish
