linux-kernel - Re: [PATCH] KVM: x86: Set BHI_NO in guest when host is not affected by BHI

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Message-ID: <18b29bd6-5eb5-4344-b80f-f6a55c18b8ba@suse.com>
Date: Thu, 11 Apr 2024 10:34:15 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: Alexandre Chartre <alexandre.chartre@...cle.com>, x86@...nel.org,
 kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, daniel.sneddon@...ux.intel.com,
 pawan.kumar.gupta@...ux.intel.com, tglx@...utronix.de,
 konrad.wilk@...cle.com, peterz@...radead.org, gregkh@...uxfoundation.org,
 seanjc@...gle.com, andrew.cooper3@...rix.com, dave.hansen@...ux.intel.com,
 kpsingh@...nel.org, longman@...hat.com, bp@...en8.de, pbonzini@...hat.com
Subject: Re: [PATCH] KVM: x86: Set BHI_NO in guest when host is not affected
 by BHI



On 11.04.24 г. 10:24 ч., Alexandre Chartre wrote:
> When a system is not affected by the BHI bug then KVM should
> configure guests with BHI_NO to ensure they won't enable any
> BHI mitigation.
> 
> Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
> ---
>   arch/x86/kvm/x86.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 984ea2089efc..f43d3c15a6b7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1678,6 +1678,9 @@ static u64 kvm_get_arch_capabilities(void)
>   	if (!boot_cpu_has_bug(X86_BUG_GDS) || gds_ucode_mitigated())
>   		data |= ARCH_CAP_GDS_NO;
>   
> +	if (!boot_cpu_has_bug(X86_BUG_BHI))
> +		data |= ARCH_CAP_BHI_NO;
> +

But this is already handled since ARCH_CAP_BHI_NO is added to 
KVM_SUPPORTED_ARCH_CAP so when the host caps are read that bit is going 
to be set there, if it's set for the physical cpu of course.
>   	return data;
>   }
>