linux-kernel - Re: [PATCH v6 1/2] x86/sev: Make sure IRQs are disabled while GHCB is active

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Date:   Thu, 17 Jun 2021 17:00:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, Joerg Roedel <jroedel@...e.de>, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Martin Radev <martin.b.radev@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v6 1/2] x86/sev: Make sure IRQs are disabled while GHCB
 is active

On Wed, Jun 16, 2021 at 08:49:12PM +0200, Joerg Roedel wrote:

>  static void sev_es_ap_hlt_loop(void)
>  {
>  	struct ghcb_state state;
> +	unsigned long flags;
>  	struct ghcb *ghcb;
>  
> -	ghcb = sev_es_get_ghcb(&state);
> +	local_irq_save(flags);
> +
> +	ghcb = __sev_get_ghcb(&state);
>  
>  	while (true) {
>  		vc_ghcb_invalidate(ghcb);
> @@ -692,7 +704,9 @@ static void sev_es_ap_hlt_loop(void)
>  			break;
>  	}
>  
> -	sev_es_put_ghcb(&state);
> +	__sev_put_ghcb(&state);
> +
> +	local_irq_restore(flags);
>  }

I think this is broken, at this point RCU is quite dead on this CPU and
local_irq_save/restore include tracing and all sorts.

Also, shouldn't IRQs already be disabled by the time we get here?