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Message-Id: <20210610091141.30322-4-joro@8bytes.org>
Date: Thu, 10 Jun 2021 11:11:38 +0200
From: Joerg Roedel <joro@...tes.org>
To: x86@...nel.org
Cc: Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
Peter Zijlstra <peterz@...radead.org>, 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: [PATCH v4 3/6] x86/sev-es: Split up runtime #VC handler for correct state tracking
From: Joerg Roedel <jroedel@...e.de>
Split up the #VC handler code into a from-user and a from-kernel part.
This allows clean and correct state tracking, as the #VC handler needs
to enter NMI-state when raised from kernel mode and plain IRQ state when
raised from user-mode.
Fixes: 62441a1fb532 ("x86/sev-es: Correctly track IRQ states in runtime #VC handler")
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
arch/x86/kernel/sev.c | 118 ++++++++++++++++++++++++------------------
1 file changed, 68 insertions(+), 50 deletions(-)
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 2a922d1b03c8..475bbc1b3547 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1326,43 +1326,14 @@ static __always_inline bool on_vc_fallback_stack(struct pt_regs *regs)
return (sp >= __this_cpu_ist_bottom_va(VC2) && sp < __this_cpu_ist_top_va(VC2));
}
-/*
- * Main #VC exception handler. It is called when the entry code was able to
- * switch off the IST to a safe kernel stack.
- *
- * With the current implementation it is always possible to switch to a safe
- * stack because #VC exceptions only happen at known places, like intercepted
- * instructions or accesses to MMIO areas/IO ports. They can also happen with
- * code instrumentation when the hypervisor intercepts #DB, but the critical
- * paths are forbidden to be instrumented, so #DB exceptions currently also
- * only happen in safe places.
- */
-DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
+static bool vc_raw_handle_exception(struct pt_regs *regs, unsigned long error_code)
{
- irqentry_state_t irq_state;
struct ghcb_state state;
struct es_em_ctxt ctxt;
enum es_result result;
unsigned long flags;
struct ghcb *ghcb;
-
- /*
- * Handle #DB before calling into !noinstr code to avoid recursive #DB.
- */
- if (error_code == SVM_EXIT_EXCP_BASE + X86_TRAP_DB) {
- vc_handle_trap_db(regs);
- return;
- }
-
- irq_state = irqentry_nmi_enter(regs);
- lockdep_assert_irqs_disabled();
- instrumentation_begin();
-
- /*
- * This is invoked through an interrupt gate, so IRQs are disabled. The
- * code below might walk page-tables for user or kernel addresses, so
- * keep the IRQs disabled to protect us against concurrent TLB flushes.
- */
+ bool ret = true;
ghcb = sev_es_get_ghcb(&state, &flags);
@@ -1382,15 +1353,18 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
case ES_UNSUPPORTED:
pr_err_ratelimited("Unsupported exit-code 0x%02lx in #VC exception (IP: 0x%lx)\n",
error_code, regs->ip);
- goto fail;
+ ret = false;
+ break;
case ES_VMM_ERROR:
pr_err_ratelimited("Failure in communication with VMM (exit-code 0x%02lx IP: 0x%lx)\n",
error_code, regs->ip);
- goto fail;
+ ret = false;
+ break;
case ES_DECODE_FAILED:
pr_err_ratelimited("Failed to decode instruction (exit-code 0x%02lx IP: 0x%lx)\n",
error_code, regs->ip);
- goto fail;
+ ret = false;
+ break;
case ES_EXCEPTION:
vc_forward_exception(&ctxt);
break;
@@ -1406,24 +1380,16 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
BUG();
}
-out:
- instrumentation_end();
- irqentry_nmi_exit(regs, irq_state);
+ return ret;
+}
- return;
+static void vc_handle_from_kernel(struct pt_regs *regs, unsigned long error_code)
+{
+ irqentry_state_t irq_state = irqentry_nmi_enter(regs);
-fail:
- if (user_mode(regs)) {
- /*
- * Do not kill the machine if user-space triggered the
- * exception. Send SIGBUS instead and let user-space deal with
- * it.
- */
- force_sig_fault(SIGBUS, BUS_OBJERR, (void __user *)0);
- } else {
- pr_emerg("PANIC: Unhandled #VC exception in kernel space (result=%d)\n",
- result);
+ instrumentation_begin();
+ if (!vc_raw_handle_exception(regs, error_code)) {
/* Show some debug info */
show_regs(regs);
@@ -1434,7 +1400,59 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
panic("Returned from Terminate-Request to Hypervisor\n");
}
- goto out;
+ instrumentation_end();
+ irqentry_nmi_exit(regs, irq_state);
+}
+
+static void vc_handle_from_user(struct pt_regs *regs, unsigned long error_code)
+{
+ irqentry_state_t irq_state = irqentry_enter(regs);
+
+ instrumentation_begin();
+
+ if (!vc_raw_handle_exception(regs, error_code)) {
+ /*
+ * Do not kill the machine if user-space triggered the
+ * exception. Send SIGBUS instead and let user-space deal with
+ * it.
+ */
+ force_sig_fault(SIGBUS, BUS_OBJERR, (void __user *)0);
+ }
+
+ instrumentation_end();
+ irqentry_exit(regs, irq_state);
+}
+/*
+ * Main #VC exception handler. It is called when the entry code was able to
+ * switch off the IST to a safe kernel stack.
+ *
+ * With the current implementation it is always possible to switch to a safe
+ * stack because #VC exceptions only happen at known places, like intercepted
+ * instructions or accesses to MMIO areas/IO ports. They can also happen with
+ * code instrumentation when the hypervisor intercepts #DB, but the critical
+ * paths are forbidden to be instrumented, so #DB exceptions currently also
+ * only happen in safe places.
+ */
+DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
+{
+ /*
+ * Handle #DB before calling into !noinstr code to avoid recursive #DB.
+ */
+ if (error_code == SVM_EXIT_EXCP_BASE + X86_TRAP_DB) {
+ vc_handle_trap_db(regs);
+ return;
+ }
+
+ /*
+ * This is invoked through an interrupt gate, so IRQs are disabled. The
+ * code below might walk page-tables for user or kernel addresses, so
+ * keep the IRQs disabled to protect us against concurrent TLB flushes.
+ */
+
+ if (user_mode(regs))
+ vc_handle_from_user(regs, error_code);
+ else
+ vc_handle_from_kernel(regs, error_code);
}
/* This handler runs on the #VC fall-back stack. It can cause further #VC exceptions */
--
2.31.1
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