[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <059c3802-9336-80bd-2e6a-36663ed099ab@redhat.com>
Date: Tue, 30 Jan 2018 18:32:52 -0500
From: Paolo Bonzini <pbonzini@...hat.com>
To: Jim Mattson <jmattson@...gle.com>,
KarimAllah Ahmed <karahmed@...zon.com>
Cc: KarimAllah Ahmed <karahmed@...zon.de>,
kvm list <kvm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>,
Asit Mallick <asit.k.mallick@...el.com>,
Arjan Van De Ven <arjan.van.de.ven@...el.com>,
Dave Hansen <dave.hansen@...el.com>,
Andi Kleen <ak@...ux.intel.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
Dan Williams <dan.j.williams@...el.com>,
Jun Nakajima <jun.nakajima@...el.com>,
David Woodhouse <dwmw@...zon.co.uk>,
Greg KH <gregkh@...uxfoundation.org>,
Andy Lutomirski <luto@...nel.org>,
Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v3 4/4] KVM: VMX: Allow direct access to
MSR_IA32_SPEC_CTRL
On 30/01/2018 17:49, Jim Mattson wrote:
> On Tue, Jan 30, 2018 at 1:00 PM, KarimAllah Ahmed <karahmed@...zon.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.
>
Let's keep the original code from David, touching the L0->L1 MSR bitmap
unconditionally, and possibly add an "&& !is_guest_mode (vcpu)" to the
condition.
Paolo
Powered by blists - more mailing lists