[PATCH v2 5/8] x86/sev-es: Leave NMI-mode before sending signals

From: Joerg Roedel <joro@8bytes.org>
To: x86@kernel.org, Hyunwook Baek <baekhw@google.com>
Cc: Joerg Roedel <joro@8bytes.org>, Joerg Roedel <jroedel@suse.de>,
	hpa@zytor.com, Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	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: [PATCH v2 5/8] x86/sev-es: Leave NMI-mode before sending signals
Date: Wed, 19 May 2021 15:52:48 +0200	[thread overview]
Message-ID: <20210519135251.30093-6-joro@8bytes.org> (raw)
In-Reply-To: <20210519135251.30093-1-joro@8bytes.org>

From: Joerg Roedel <jroedel@suse.de>

The error path in the runtime #VC handler sends a signal to kill the
current task if the exception was raised from user-space. Some parts of
the #VC handler run in NMI mode, because it is critical that it is not
interrupted (except from an NMI) while the GHCB is in use.

But sending signals in NMI-mode is actually broken and triggers lockdep
warnings. On the other side, when the signal is sent, there is no reason
for the handler to still be in NMI-mode, as the GHCB is not used
anymore.

Leave NMI-mode before entering the error path to get rid of the lockdep
warnings.

Fixes: 62441a1fb532 ("x86/sev-es: Correctly track IRQ states in runtime #VC handler")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kernel/sev.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 4fd997bbf059..9a64030e74c0 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1343,9 +1343,10 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 		return;
 	}
 
+	instrumentation_begin();
+
 	irq_state = irqentry_nmi_enter(regs);
 	lockdep_assert_irqs_disabled();
-	instrumentation_begin();
 
 	/*
 	 * This is invoked through an interrupt gate, so IRQs are disabled. The
@@ -1395,13 +1396,19 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 		BUG();
 	}
 
-out:
-	instrumentation_end();
 	irqentry_nmi_exit(regs, irq_state);
+	instrumentation_end();
 
 	return;
 
 fail:
+	/*
+	 * Leave NMI mode - the GHCB is not busy anymore and depending on where
+	 * the #VC came from this code is about to either kill the task (when in
+	 * task context) or kill the machine.
+	 */
+	irqentry_nmi_exit(regs, irq_state);
+
 	if (user_mode(regs)) {
 		/*
 		 * Do not kill the machine if user-space triggered the
@@ -1423,7 +1430,9 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 		panic("Returned from Terminate-Request to Hypervisor\n");
 	}
 
-	goto out;
+	instrumentation_end();
+
+	return;
 }
 
 /* This handler runs on the #VC fall-back stack. It can cause further #VC exceptions */
-- 
2.31.1

