linux-kernel - [PATCH v4 63/75] x86/sev-es: Handle #DB Events

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Message-Id: <20200714120917.11253-64-joro@8bytes.org>
Date:   Tue, 14 Jul 2020 14:09:05 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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 <sean.j.christopherson@...el.com>,
        Martin Radev <martin.b.radev@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH v4 63/75] x86/sev-es: Handle #DB Events

From: Joerg Roedel <jroedel@...e.de>

Handle #VC exceptions caused by #DB exceptions in the guest. Those
must be handled outside of instrumentation_begin()/end() so that the
handler will not be raised recursivly.

Handle them by calling the kernels debug exception handler.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/kernel/sev-es.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 8f275e5d1ce7..b0f08d9669f1 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -928,6 +928,14 @@ static enum es_result vc_handle_trap_ac(struct ghcb *ghcb,
 	return ES_EXCEPTION;
 }
 
+static __always_inline void vc_handle_trap_db(struct pt_regs *regs)
+{
+	if (user_mode(regs))
+		noist_exc_debug(regs);
+	else
+		exc_debug(regs);
+}
+
 static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
 					 struct ghcb *ghcb,
 					 unsigned long exit_code)
@@ -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();
 
 	/*
-- 
2.27.0