[PATCH v2 10/13] powerpc/pseries/svm: Disable doorbells in SVM guests

Thiago Jung Bauermann bauerman at linux.ibm.com
Sat Jul 13 16:00:20 AEST 2019

From: Sukadev Bhattiprolu <sukadev at linux.ibm.com>

Normally, the HV emulates some instructions like MSGSNDP, MSGCLRP
from a KVM guest. To emulate the instructions, it must first read
the instruction from the guest's memory and decode its parameters.

However for a secure guest (aka SVM), the page containing the
instruction is in secure memory and the HV cannot access directly.
It would need the Ultravisor (UV) to facilitate accessing the
instruction and parameters but the UV currently does not have
the support for such accesses.

Until the UV has such support, disable doorbells in SVMs. This might
incur a performance hit but that is yet to be quantified.

With this patch applied (needed only in SVMs not needed for HV) we
are able to launch SVM guests with multi-core support. Eg:

	qemu -smp sockets=2,cores=2,threads=2.

Fix suggested by Benjamin Herrenschmidt. Thanks to input from
Paul Mackerras, Ram Pai and Michael Anderson.

Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman at linux.ibm.com>
 arch/powerpc/platforms/pseries/smp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/smp.c b/arch/powerpc/platforms/pseries/smp.c
index 3df46123cce3..95a5c24a1544 100644
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -45,6 +45,7 @@
 #include <asm/dbell.h>
 #include <asm/plpar_wrappers.h>
 #include <asm/code-patching.h>
+#include <asm/svm.h>
 #include "pseries.h"
 #include "offline_states.h"
@@ -225,7 +226,7 @@ static __init void pSeries_smp_probe_xics(void)
-	if (cpu_has_feature(CPU_FTR_DBELL))
+	if (cpu_has_feature(CPU_FTR_DBELL) && !is_secure_guest())
 		smp_ops->cause_ipi = smp_pseries_cause_ipi;
 		smp_ops->cause_ipi = icp_ops->cause_ipi;

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