linux-kernel - [PATCH v3 12/16] powerpc/pseries/svm: Disable doorbells in SVM guests

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Date:   Tue,  6 Aug 2019 02:22:33 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, Alexey Kardashevskiy <aik@...abs.ru>,
        Anshuman Khandual <anshuman.linux@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mike Anderson <andmike@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Ram Pai <linuxram@...ibm.com>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>,
        Sukadev Bhattiprolu <sukadev@...ux.ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Subject: [PATCH v3 12/16] powerpc/pseries/svm: Disable doorbells in SVM guests

From: Sukadev Bhattiprolu <sukadev@...ux.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@...ux.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.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 4b3ef8d9c63f..ad61e90032da 100644
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -41,6 +41,7 @@
 #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"
@@ -221,7 +222,7 @@ static __init void pSeries_smp_probe_xics(void)
 {
 	xics_smp_probe();

-	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;
 	else
 		smp_ops->cause_ipi = icp_ops->cause_ipi;