linux-kernel - Re: [PATCH v5 22/26] KVM: VMX: Move LOAD_IA32_PERF_GLOBAL_CTRL errata handling out of setup_vmcs

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: <Yv57tmu09nOQcFrf@google.com>
Date:   Thu, 18 Aug 2022 17:49:42 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 22/26] KVM: VMX: Move LOAD_IA32_PERF_GLOBAL_CTRL
 errata handling out of setup_vmcs_config()

On Tue, Aug 02, 2022, Vitaly Kuznetsov wrote:
> While it seems reasonable to not expose LOAD_IA32_PERF_GLOBAL_CTRL controls
> to L1 hypervisor on buggy CPUs, such change would inevitably break live
> migration from older KVMs where the controls are exposed. Keep the status quo
> for now, L1 hypervisor itself is supposed to take care of the errata.

As noted before, this statement is wrong as it requires guest FMS == host FMS,
but it's irrelevant because KVM can emulate the control unconditionally.  I'll
test and fold in my suggested patch[*] (assuming it works) and reword this part
of the changelog.  Ah, and I'll also need to fold in a patch to actually emulate
the controls without hardware support.

[*] https://lore.kernel.org/all/YtnZmCutdd5tpUmz@google.com

> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 59 +++++++++++++++++++++++++-----------------
>  1 file changed, 35 insertions(+), 24 deletions(-)
> 

...

> @@ -8192,6 +8199,10 @@ static __init int hardware_setup(void)
>  	if (setup_vmcs_config(&vmcs_config, &vmx_capability) < 0)
>  		return -EIO;
>  
> +	if (cpu_has_perf_global_ctrl_bug())
> +		pr_warn_once("kvm: VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL "
> +			     "does not work properly. Using workaround\n");

Any objections to opportunistically tweaking this?

		pr_warn_once("kvm: CPU has VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL erratum,"
			     "using MSR load/store lists for PERF_GLOBAL_CTRL\n");

> +
>  	if (boot_cpu_has(X86_FEATURE_NX))
>  		kvm_enable_efer_bits(EFER_NX);
>  
> -- 
> 2.35.3
>