linux-kernel - Re: [PATCH v2 1/4] x86/bugs: Add SRSO_USER_KERNEL

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Message-ID: <20241210065331.ojnespi77no7kfqf@jpoimboe>
Date: Mon, 9 Dec 2024 22:53:31 -0800
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Borislav Petkov <bp@...nel.org>
Cc: Sean Christopherson <seanjc@...gle.com>, X86 ML <x86@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	KVM <kvm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
	"Borislav Petkov (AMD)" <bp@...en8.de>
Subject: Re: [PATCH v2 1/4] x86/bugs: Add SRSO_USER_KERNEL_NO support

On Mon, Dec 02, 2024 at 01:04:13PM +0100, Borislav Petkov wrote:
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -2615,6 +2615,11 @@ static void __init srso_select_mitigation(void)
>  		break;
>  
>  	case SRSO_CMD_SAFE_RET:
> +		if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO)) {
> +			pr_notice("CPU user/kernel transitions protected, falling back to IBPB-on-VMEXIT\n");
> +			goto ibpb_on_vmexit;

The presence of SRSO_USER_KERNEL_NO should indeed change the default,
but if the user requests "safe_ret" specifically, shouldn't we give it
to them?  That would be more consistent with how we handle requested
mitigations.

Also it doesn't really make sense to add a printk here as the mitigation
will be printed at the end of the function.

-- 
Josh