On Wed, Aug 12, 2020 at 10:42 PM Chenyi Qiang <chenyi.qiang@xxxxxxxxx> wrote: > > > > On 8/13/2020 5:21 AM, Jim Mattson wrote: > > On Fri, Aug 7, 2020 at 1:46 AM Chenyi Qiang <chenyi.qiang@xxxxxxxxx> 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@xxxxxxxxx> > >> --- > > > >> 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.
