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Date:   Wed, 15 Jul 2020 10:47:52 +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 <sean.j.christopherson@intel.com>,
        Martin Radev <martin.b.radev@gmail.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v4 63/75] x86/sev-es: Handle #DB Events
Message-ID: <20200715084752.GD10769@hirez.programming.kicks-ass.net>
References: <20200714120917.11253-1-joro@8bytes.org>
 <20200714120917.11253-64-joro@8bytes.org>
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On Tue, Jul 14, 2020 at 02:09:05PM +0200, Joerg Roedel wrote:

> @@ -1028,6 +1036,16 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
>  	struct ghcb *ghcb;
>  
>  	lockdep_assert_irqs_disabled();
> +
> +	/*
> +	 * #DB is special and needs to be handled outside of the intrumentation_begin()/end().
> +	 * Otherwise the #VC handler could be raised recursivly.
> +	 */
> +	if (error_code == SVM_EXIT_EXCP_BASE + X86_TRAP_DB) {
> +		vc_handle_trap_db(regs);
> +		return;
> +	}
> +
>  	instrumentation_begin();

Wait what?! That makes no sense what so ever.