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Date: Thu, 17 Jun 2021 17:00:48 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Joerg Roedel <joro@8bytes.org>
Cc: x86@kernel.org, Joerg Roedel <jroedel@suse.de>, hpa@zytor.com,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Jiri Slaby <jslaby@suse.cz>,
	Dan Williams <dan.j.williams@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Juergen Gross <jgross@suse.com>, Kees Cook <keescook@chromium.org>,
	David Rientjes <rientjes@google.com>, Cfir Cohen <cfir@google.com>,
	Erdem Aktas <erdemaktas@google.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mike Stunes <mstunes@vmware.com>,
	Sean Christopherson <seanjc@google.com>,
	Martin Radev <martin.b.radev@gmail.com>,
	Arvind Sankar <nivedita@alum.mit.edu>, linux-coco@lists.linux.dev,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v6 1/2] x86/sev: Make sure IRQs are disabled while GHCB
 is active
Message-ID: <YMtjoLLQpKyveVlS@hirez.programming.kicks-ass.net>
References: <20210616184913.13064-1-joro@8bytes.org>
 <20210616184913.13064-2-joro@8bytes.org>
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In-Reply-To: <20210616184913.13064-2-joro@8bytes.org>

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?