From 9452246e59a5f16f44fdf9a7d514b947faf1d5fc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= <clg@redhat.com>
Date: Mon, 16 Jan 2023 18:46:05 +0100
Subject: [PATCH 5/9] s390x/pv: Implement a CGS check helper
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RH-Author: Cédric Le Goater <clg@redhat.com>
RH-MergeRequest: 139: s390x/pv: Implement a CGS check helper
RH-Bugzilla: 2122523
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
RH-Acked-by: David Hildenbrand <david@redhat.com>
RH-Commit: [1/1] 8551ce772b10de653b4e1c8be60aae60ec98b421 (clegoate/qemu-kvm-c9s)

When a protected VM is started with the maximum number of CPUs (248),
the service call providing information on the CPUs requires more
buffer space than allocated and QEMU disgracefully aborts :

    LOADPARM=[........]
    Using virtio-blk.
    Using SCSI scheme.
    ...................................................................................
    qemu-system-s390x: KVM_S390_MEM_OP failed: Argument list too long

When protected virtualization is initialized, compute the maximum
number of vCPUs supported by the machine and return useful information
to the user before the machine starts in case of error.

Suggested-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Message-Id: <20230116174607.2459498-2-clg@kaod.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit 75d7150c636569f6687f7e70a33be893be43eb5f)
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 hw/s390x/pv.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/hw/s390x/pv.c b/hw/s390x/pv.c
index 8dfe92d8df..8a1c71436b 100644
--- a/hw/s390x/pv.c
+++ b/hw/s390x/pv.c
@@ -20,6 +20,7 @@
 #include "exec/confidential-guest-support.h"
 #include "hw/s390x/ipl.h"
 #include "hw/s390x/pv.h"
+#include "hw/s390x/sclp.h"
 #include "target/s390x/kvm/kvm_s390x.h"
 
 static bool info_valid;
@@ -249,6 +250,41 @@ struct S390PVGuestClass {
     ConfidentialGuestSupportClass parent_class;
 };
 
+/*
+ * If protected virtualization is enabled, the amount of data that the
+ * Read SCP Info Service Call can use is limited to one page. The
+ * available space also depends on the Extended-Length SCCB (ELS)
+ * feature which can take more buffer space to store feature
+ * information. This impacts the maximum number of CPUs supported in
+ * the machine.
+ */
+static uint32_t s390_pv_get_max_cpus(void)
+{
+    int offset_cpu = s390_has_feat(S390_FEAT_EXTENDED_LENGTH_SCCB) ?
+        offsetof(ReadInfo, entries) : SCLP_READ_SCP_INFO_FIXED_CPU_OFFSET;
+
+    return (TARGET_PAGE_SIZE - offset_cpu) / sizeof(CPUEntry);
+}
+
+static bool s390_pv_check_cpus(Error **errp)
+{
+    MachineState *ms = MACHINE(qdev_get_machine());
+    uint32_t pv_max_cpus = s390_pv_get_max_cpus();
+
+    if (ms->smp.max_cpus > pv_max_cpus) {
+        error_setg(errp, "Protected VMs support a maximum of %d CPUs",
+                   pv_max_cpus);
+        return false;
+    }
+
+    return true;
+}
+
+static bool s390_pv_guest_check(ConfidentialGuestSupport *cgs, Error **errp)
+{
+    return s390_pv_check_cpus(errp);
+}
+
 int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
 {
     if (!object_dynamic_cast(OBJECT(cgs), TYPE_S390_PV_GUEST)) {
@@ -261,6 +297,10 @@ int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
         return -1;
     }
 
+    if (!s390_pv_guest_check(cgs, errp)) {
+        return -1;
+    }
+
     cgs->ready = true;
 
     return 0;
-- 
2.31.1