@@ -91,8 +91,10 @@
//
// IO ports
//
-#define ICH9_APM_CNT 0xB2
-#define ICH9_APM_STS 0xB3
+#define ICH9_APM_CNT 0xB2
+
+#define ICH9_APM_STS 0xB3
+#define QEMU_ICH9_APM_STS_BROADCAST_SMI 'Q'
//
// IO ports relative to PMBASE
@@ -107,10 +107,26 @@ SmmControl2DxeTrigger (
// report about hardware status, while this register is fully governed by
// software.
//
+ // On the QEMU platform, we use the status register to request a "broadcast"
+ // SMI; i.e., to bring all VCPUs into SMM at once. Edk2 handles the case when
+ // the SMI is raised only on the processor that calls Trigger(), but
+ //
+ // - if the processor executing Trigger() is an AP, then the resultant AP-BSP
+ // synchronization is time consuming and computation-hungry,
+ //
+ // - edk2 modules that deal with SMIs generally expect / prefer a software
+ // SMI to affect all CPUs at once; unicast SMIs have exposed obscure corner
+ // cases.
+ //
+ // Note that we exploit the fact that the SMM_CORE never passes a non-NULL
+ // DataPort pointer (that is, we exploit that it doesn't care about the
+ // status register value).
+ //
// Write to the status register first, as this won't trigger the SMI just
// yet. Then write to the control register.
//
- IoWrite8 (ICH9_APM_STS, DataPort == NULL ? 0 : *DataPort);
+ ASSERT (DataPort == NULL);
+ IoWrite8 (ICH9_APM_STS, QEMU_ICH9_APM_STS_BROADCAST_SMI);
IoWrite8 (ICH9_APM_CNT, CommandPort == NULL ? 0 : *CommandPort);
return EFI_SUCCESS;
}
When writing to IO port 0xB2 (ICH9_APM_CNT), QEMU by default injects an SMI only on the VCPU that is writing the port. This has exposed corner cases and strange behavior with edk2 code, which generally expects a software SMI to affect all CPUs at once. The QEMU patch hw/isa/lpc_ich9: inject SMI on all VCPUs if APM_STS == 'Q' adds a side-channel / backdoor to QEMU that enables the firmware to request a broadcast SMI; namely, by setting IO port 0xB3 (ICH9_APM_STS) to value 0x51 ('Q') first. (The default behavior cannot be changed because SeaBIOS depends on it.) Utilize this feature in OVMF's EFI_SMM_CONTROL2_PROTOCOL.Trigger() method. The change has no effect on QEMUs that lack the above patch. Cc: Jordan Justen <jordan.l.justen@intel.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=230 Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Laszlo Ersek <lersek@redhat.com> --- OvmfPkg/Include/IndustryStandard/Q35MchIch9.h | 6 ++++-- OvmfPkg/SmmControl2Dxe/SmmControl2Dxe.c | 18 +++++++++++++++++- 2 files changed, 21 insertions(+), 3 deletions(-) -- 2.9.2 _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel