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Date:   Tue, 17 Nov 2020 19:28:09 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Alexandre Chartre <alexandre.chartre@oracle.com>
Cc:     tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
        x86@kernel.org, dave.hansen@linux.intel.com, luto@kernel.org,
        peterz@infradead.org, linux-kernel@vger.kernel.org,
        thomas.lendacky@amd.com, jroedel@suse.de, konrad.wilk@oracle.com,
        jan.setjeeilers@oracle.com, junaids@google.com, oweisse@google.com,
        rppt@linux.vnet.ibm.com, graf@amazon.de, mgross@linux.intel.com,
        kuzuno@gmail.com
Subject: Re: [RFC][PATCH v2 00/21] x86/pti: Defer CR3 switch to C code
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On Tue, Nov 17, 2020 at 07:12:07PM +0100, Alexandre Chartre wrote:
> Yes. L1TF/MDS allow some inter cpu-thread attacks which are not mitigated at
> the moment. In particular, this allows a guest VM to attack another guest VM
> or the host kernel running on a sibling cpu-thread. Core Scheduling will
> mitigate the guest-to-guest attack but not the guest-to-host attack.

I see in vmx_vcpu_enter_exit():

        /* L1D Flush includes CPU buffer clear to mitigate MDS */
        if (static_branch_unlikely(&vmx_l1d_should_flush))
                vmx_l1d_flush(vcpu);
        else if (static_branch_unlikely(&mds_user_clear))
                mds_clear_cpu_buffers();

Is that not enough?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette