Messages in this thread | | | Subject | Re: [PATCH v3 4/4] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL | From | KarimAllah Ahmed <> | Date | Wed, 31 Jan 2018 00:50:17 +0100 |
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On 01/30/2018 11:49 PM, Jim Mattson wrote: > On Tue, Jan 30, 2018 at 1:00 PM, KarimAllah Ahmed <karahmed@amazon.com> wrote: >> Ooops! I did not think at all about nested :) >> >> This should be addressed now, I hope: >> >> http://git.infradead.org/linux-retpoline.git/commitdiff/f7f0cbba3e0cffcee050a8a5a9597a162d57e572 > > + if (cpu_has_vmx_msr_bitmap() && data && > + !vmx->save_spec_ctrl_on_exit) { > + vmx->save_spec_ctrl_on_exit = true; > + > + msr_bitmap = is_guest_mode(vcpu) ? > vmx->nested.vmcs02.msr_bitmap : > + > vmx->vmcs01.msr_bitmap; > + vmx_disable_intercept_for_msr(msr_bitmap, > + MSR_IA32_SPEC_CTRL, > + MSR_TYPE_RW); > + } > > There are two ways to get to this point in vmx_set_msr while > is_guest_mode(vcpu) is true: > 1) L0 is processing vmcs12's VM-entry MSR load list on emulated > VM-entry (see enter_vmx_non_root_mode). > 2) L2 tried to execute WRMSR, writes to the MSR are intercepted in > vmcs02's MSR permission bitmap, and writes to the MSR are not > intercepted in vmcs12's MSR permission bitmap. > > In the first case, disabling the intercepts for the MSR in > vmx->nested.vmcs02.msr_bitmap is incorrect, because we haven't yet > determined that the intercepts are clear in vmcs12's MSR permission > bitmap. > In the second case, disabling *both* of the intercepts for the MSR in > vmx->nested.vmcs02.msr_bitmap is incorrect, because we don't know that > the read intercept is clear in vmcs12's MSR permission bitmap. > Furthermore, disabling the write intercept for the MSR in > vmx->nested.vmcs02.msr_bitmap is somewhat fruitless, because > nested_vmx_merge_msr_bitmap is just going to undo that change on the > next emulated VM-entry.
Okay, I took a second look at the code (specially nested_vmx_merge_msr_bitmap).
This means that I simply should not touch the MSR bitmap in set_msr in case of nested, I just need to properly update the l02 msr_bitmap in nested_vmx_merge_msr_bitmap. As in here:
http://git.infradead.org/linux-retpoline.git/commitdiff/d90eedebdd16bb00741a2c93bc13c5e444c99c2b
or am I still missing something? (sorry, did not actually look at the nested code before!)
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