On Tue, Aug 18, 2020 at 11:23:47AM -0700, Jim Mattson wrote: > On Tue, Aug 18, 2020 at 12:28 AM Chenyi Qiang <chenyi.qi...@intel.com> wrote: > > > > > > > > On 8/14/2020 1:31 AM, Jim Mattson wrote: > > > On Wed, Aug 12, 2020 at 10:42 PM Chenyi Qiang <chenyi.qi...@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.qi...@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.qi...@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? > > I'll let someone who actually cares about the i386 build answer that question.
Ha, I care about the i386 build to the extent that it doesn't break. I don't care at all shaving cycles/memory for things like this. Given how long some KVM i386 bugs have gone unnoticed I'm not sure there's anyone that cares about KVM i386 these days :-)
