Messages in this thread | | | Subject | Re: [RFC 2/7] KVM: VMX: Expose IA32_PKRS MSR | From | Chenyi Qiang <> | Date | Tue, 18 Aug 2020 15:27:51 +0800 |
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On 8/14/2020 1:31 AM, Jim Mattson wrote: > On Wed, Aug 12, 2020 at 10:42 PM Chenyi Qiang <chenyi.qiang@intel.com> wrote: >> >> >> >> On 8/13/2020 5:21 AM, Jim Mattson wrote: >>> On Fri, Aug 7, 2020 at 1:46 AM Chenyi Qiang <chenyi.qiang@intel.com> wrote: >>>> >>>> Protection Keys for Supervisor Pages (PKS) uses IA32_PKRS MSR (PKRS) at >>>> index 0x6E1 to allow software to manage supervisor protection key >>>> rights. For performance consideration, PKRS intercept will be disabled >>>> so that the guest can access the PKRS without VM exits. >>>> PKS introduces dedicated control fields in VMCS to switch PKRS, which >>>> only does the retore part. In addition, every VM exit saves PKRS into >>>> the guest-state area in VMCS, while VM enter won't save the host value >>>> due to the expectation that the host won't change the MSR often. Update >>>> the host's value in VMCS manually if the MSR has been changed by the >>>> kernel since the last time the VMCS was run. >>>> The function get_current_pkrs() in arch/x86/mm/pkeys.c exports the >>>> per-cpu variable pkrs_cache to avoid frequent rdmsr of PKRS. >>>> >>>> Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com> >>>> --- >>> >>>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c >>>> index 11e4df560018..df2c2e733549 100644 >>>> --- a/arch/x86/kvm/vmx/nested.c >>>> +++ b/arch/x86/kvm/vmx/nested.c >>>> @@ -289,6 +289,7 @@ static void vmx_sync_vmcs_host_state(struct vcpu_vmx *vmx, >>>> dest->ds_sel = src->ds_sel; >>>> dest->es_sel = src->es_sel; >>>> #endif >>>> + dest->pkrs = src->pkrs; >>> >>> Why isn't this (and other PKRS code) inside the #ifdef CONFIG_X86_64? >>> PKRS isn't usable outside of long mode, is it? >>> >> >> Yes, I'm also thinking about whether to put all pks code into >> CONFIG_X86_64. The kernel implementation also wrap its pks code inside >> CONFIG_ARCH_HAS_SUPERVISOR_PKEYS which has dependency with CONFIG_X86_64. >> However, maybe this can help when host kernel disable PKS but the guest >> enable it. What do you think about this? > > I see no problem in exposing PKRS to the guest even if the host > doesn't have CONFIG_ARCH_HAS_SUPERVISOR_PKEYS. >
Yes, but I would prefer to keep it outside CONFIG_X86_64. PKS code has several code blocks and putting them under x86_64 may end up being a mess. In addition, PKU KVM related code isn't under CONFIG_X86_64 as well. So, is it really necessary to put inside?
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