On 8/26/22 12:15, Ross Lagerwall wrote:
From: Stefan Berger <stef...@linux.ibm.com>
Sent: Friday, August 26, 2022 4:20 PM
To: Ross Lagerwall <ross.lagerw...@citrix.com>; Stefan Berger
<stef...@linux.vnet.ibm.com>
Cc: qemu-devel@nongnu.org <qemu-devel@nongnu.org>
Subject: Re: [PATCH] tpm_crb: Avoid backend startup just before shutdown under
Xen
On 8/26/22 10:38, Ross Lagerwall wrote:
When running under Xen and the guest reboots, it boots into a new domain
with a new QEMU process (and a new swtpm process if using the emulator
backend). The existing reset function is triggered just before the old
QEMU process exists which causes QEMU to startup the TPM backend and
then immediately shut it down. This is probably harmless but when using
the emulated backend, it wastes CPU and IO time reloading state, etc.
Fix this by calling the reset function directly from realize() when
running under Xen. During a reboot, this will be called by the QEMU
process for the new domain.
Signed-off-by: Ross Lagerwall <ross.lagerw...@citrix.com>
---
This conditional logic is ugly. Is there a cleaner way of doing this?
hw/tpm/tpm_crb.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/hw/tpm/tpm_crb.c b/hw/tpm/tpm_crb.c
index 67db594c48..ea930da545 100644
--- a/hw/tpm/tpm_crb.c
+++ b/hw/tpm/tpm_crb.c
@@ -26,6 +26,7 @@
#include "sysemu/tpm_backend.h"
#include "sysemu/tpm_util.h"
#include "sysemu/reset.h"
+#include "sysemu/xen.h"
#include "tpm_prop.h"
#include "tpm_ppi.h"
#include "trace.h"
@@ -308,7 +309,11 @@ static void tpm_crb_realize(DeviceState *dev, Error **errp)
TPM_PPI_ADDR_BASE, OBJECT(s));
}
- qemu_register_reset(tpm_crb_reset, dev);
+ if (xen_enabled()) {
+ tpm_crb_reset(dev);
+ } else {
+ qemu_register_reset(tpm_crb_reset, dev);
+ }
}
static void tpm_crb_class_init(ObjectClass *klass, void *data)
This doesn't look right also for Xen. Shouldn't it be something like this?
qemu_register_reset(tpm_crb_reset, dev);
if (xen_enabled()) {
tpm_crb_reset(dev);
}
We need the reset callback for VM reset.
This patch doesn't change anything for the QEMU/KVM case which works
fine as is.
In the Xen architecture, the guest is rebooted into a new domain which
has new instances of QEMU and swtpm. The old instances are terminated.
So during a guest reboot it doesn't make sense to have the QEMU for the
old domain call tpm_crb_reset() just as it is about to exit since it
causes swtpm to be sent CMD_INIT which causes it to needlessly
reinitialize and reload the state. Instead, the new QEMU instance
post-reboot will call tpm_crb_reset() to start the backend directly from
the realize() function, just as for the initial guest boot.
You should probably add this to the commit text because I wouldn't have
known that a VM reset in Xen causes a new domain to be created...
Ross
