Re: [PATCH v5 3/6] x86/sev-es: Split up runtime #VC handler for correct state tracking
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-06-16 16:23:07
Also in:
kvm, lkml, virtualization
On Mon, Jun 14, 2021 at 03:53:24PM +0200, Joerg Roedel wrote:
quoted hunk ↗ jump to hunk
--- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S@@ -506,7 +506,7 @@ SYM_CODE_START(\asmsym) movq %rsp, %rdi /* pt_regs pointer */ - call \cfunc + call kernel_\cfunc /* * No need to switch back to the IST stack. The current stack is either@@ -517,7 +517,7 @@ SYM_CODE_START(\asmsym) /* Switch to the regular task stack */ .Lfrom_usermode_switch_stack_\@: - idtentry_body safe_stack_\cfunc, has_error_code=1 + idtentry_body user_\cfunc, has_error_code=1 _ASM_NOKPROBE(\asmsym) SYM_CODE_END(\asmsym)
Consistency with idtentry_mce_db would seem to suggest using \cfunc and noist_\cfunc. amluto, tglx: do we have strong feelings on consistency?
+static bool noinstr vc_check_and_handle_db(struct pt_regs *regs, unsigned long error_code)
+{
+ if (likely(error_code != SVM_EXIT_EXCP_BASE + X86_TRAP_DB))
+ return false;
+ vc_handle_trap_db(regs);It's a bit sad this does user_mode(regs) again.
+ + return true; +}
Maybe something like:
static __always_inline bool vc_is_db(unsigned long error_code)
{
return error_code == SVM_EXIT_EXCP_BASE + X86_TRAP_DB;
}
+
+/*
+ * Runtime #VC exception handler when raised from kernel mode. Runs in NMI mode
+ * and will panic when an error happens.
+ */
+DEFINE_IDTENTRY_VC_KERNEL(exc_vmm_communication)
+{
+ irqentry_state_t irq_state;
+ /*
+ * 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.
+ *
+ * But keep this here in case the noinstr annotations are violated due
+ * to bug elsewhere.
+ */
+ if (unlikely(on_vc_fallback_stack(regs))) {
+ instrumentation_begin();
+ panic("Can't handle #VC exception from unsupported context\n");
+ instrumentation_end();
+ }
+
+ /*
+ * Handle #DB before calling into !noinstr code to avoid recursive #DB.
+ */
+ if (vc_check_and_handle_db(regs, error_code))
+ return;
if (vc_is_db(error_core)) {
exc_debug(regs);
return;
}
quoted hunk ↗ jump to hunk
+ + irq_state = irqentry_nmi_enter(regs); + + instrumentation_begin(); + + if (!vc_raw_handle_exception(regs, error_code)) { /* Show some debug info */ show_regs(regs);@@ -1443,23 +1448,38 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication) panic("Returned from Terminate-Request to Hypervisor\n"); } + instrumentation_end(); + irqentry_nmi_exit(regs, irq_state); } +/* + * Runtime #VC exception handler when raised from user mode. Runs in IRQ mode + * and will kill the current task with SIGBUS when an error happens. + */ +DEFINE_IDTENTRY_VC_USER(exc_vmm_communication) { + irqentry_state_t irq_state; + + /* + * Handle #DB before calling into !noinstr code to avoid recursive #DB. + */ + if (vc_check_and_handle_db(regs, error_code)) + return;
if (vs_is_db(error_code)) {
noist_exc_debug(regs);
return;
}
+
+ 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);
}Other than that, this seems *much* nicer. Thanks!