linux-kernel - Re: [PATCH v13 00/12] Add AMD SEV guest live migration support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CABayD+dGWWha8opC7rFgNYs=bgWbohE+ngTRfKjw12fXrT+Q+g@mail.gmail.com>
Date:   Fri, 16 Apr 2021 14:43:48 -0700
From:   Steve Rutherford <srutherford@...gle.com>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        Borislav Petkov <bp@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        X86 ML <x86@...nel.org>, KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Venu Busireddy <venu.busireddy@...cle.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v13 00/12] Add AMD SEV guest live migration support

On Thu, Apr 15, 2021 at 8:52 AM Ashish Kalra <Ashish.Kalra@....com> wrote:
>
> From: Ashish Kalra <ashish.kalra@....com>
>
> The series add support for AMD SEV guest live migration commands. To protect the
> confidentiality of an SEV protected guest memory while in transit we need to
> use the SEV commands defined in SEV API spec [1].
>
> SEV guest VMs have the concept of private and shared memory. Private memory
> is encrypted with the guest-specific key, while shared memory may be encrypted
> with hypervisor key. The commands provided by the SEV FW are meant to be used
> for the private memory only. The patch series introduces a new hypercall.
> The guest OS can use this hypercall to notify the page encryption status.
> If the page is encrypted with guest specific-key then we use SEV command during
> the migration. If page is not encrypted then fallback to default.
>
> The patch uses the KVM_EXIT_HYPERCALL exitcode and hypercall to
> userspace exit functionality as a common interface from the guest back to the
> VMM and passing on the guest shared/unencrypted page information to the
> userspace VMM/Qemu. Qemu can consult this information during migration to know
> whether the page is encrypted.
>
> This section descibes how the SEV live migration feature is negotiated
> between the host and guest, the host indicates this feature support via
> KVM_FEATURE_CPUID. The guest firmware (OVMF) detects this feature and
> sets a UEFI enviroment variable indicating OVMF support for live
> migration, the guest kernel also detects the host support for this
> feature via cpuid and in case of an EFI boot verifies if OVMF also
> supports this feature by getting the UEFI enviroment variable and if it
> set then enables live migration feature on host by writing to a custom
> MSR, if not booted under EFI, then it simply enables the feature by
> again writing to the custom MSR. The MSR is also handled by the
> userspace VMM/Qemu.
>
> A branch containing these patches is available here:
> https://github.com/AMDESE/linux/tree/sev-migration-v13
>
> [1] https://developer.amd.com/wp-content/resources/55766.PDF
>
> Changes since v12:
> - Reset page encryption status during early boot instead of just
>   before the kexec to avoid SMP races during kvm_pv_guest_cpu_reboot().

Does this series need to disable the MSR during kvm_pv_guest_cpu_reboot()?

I _think_ going into blackout during the window after restart, but
before the MSR is explicitly reenabled, would cause corruption. The
historical shared pages could be re-allocated as non-shared pages
during restart.

Steve