On 1/5/23 14:58, Claudio Imbrenda wrote:
On Thu, 5 Jan 2023 12:42:54 +0100
Thomas Huth <th...@redhat.com> wrote:
On 04/01/2023 12.51, Cédric Le Goater wrote:
From: Cédric Le Goater <c...@redhat.com>
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
Implement a test for this limitation in the ConfidentialGuestSupportClass
check handler and provide some valid information to the user before the
machine starts.
Signed-off-by: Cédric Le Goater <c...@redhat.com>
---
hw/s390x/pv.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/hw/s390x/pv.c b/hw/s390x/pv.c
index 8dfe92d8df..3a7ec70634 100644
--- a/hw/s390x/pv.c
+++ b/hw/s390x/pv.c
@@ -266,6 +266,26 @@ int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error
**errp)
return 0;
}
+static bool s390_pv_check_cpus(Error **errp)
+{
+ MachineState *ms = MACHINE(qdev_get_machine());
+ MachineClass *mc = MACHINE_GET_CLASS(ms);
+ uint32_t pv_max_cpus = mc->max_cpus - 1;
Not sure whether "mc->max_cpus - 1" is the right approach here. I think it
would be better to calculate the amount of CPUs that we can support.
So AFAIK the problem is that SCLP information that is gathered during
read_SCP_info() in hw/s390x/sclp.c. If protected virtualization is enabled,
everything has to fit in one page (i.e. 4096 bytes) there.
So we have space for
(TARGET_PAGE_SIZE - offset_cpu) / sizeof(CPUEntry)
CPUs.
With S390_FEAT_EXTENDED_LENGTH_SCCB enabled, offset_cpu is 144 (see struct
ReadInfo in sclp.h), otherwise it is 128.
That means, with S390_FEAT_EXTENDED_LENGTH_SCCB we can have a maximum of:
(4096 - 144) / 16 = 247 CPUs
which is what you were trying to check with the mc->max_cpus - 1 here.
yes. That's much better.
But with "-cpu els=off", it sounds like we could fit all 248 also with
protected VMs? Could you please give it a try?
It runs. Unfortunately, QEMU also complains with :
qemu-system-s390x: warning: 'diag318' requires 'els'.
qemu-system-s390x: warning: 'diag318' requires 'els'.
qemu-system-s390x: warning: 'diag318' requires 'els'.
when els is off.
Anyway, instead of using "pv_max_cpus = mc->max_cpus - 1" I'd suggest to use
something like this instead:
int offset_cpu = s390_has_feat(S390_FEAT_EXTENDED_LENGTH_SCCB) ?
offsetof(ReadInfo, entries) :
SCLP_READ_SCP_INFO_FIXED_CPU_OFFSET;
pv_max_cpus = (TARGET_PAGE_SIZE - offset_cpu) /sizeof(CPUEntry);
I agree with Thomas here
The problem is that QEMU doesn't know about the S390_FEAT_EXTENDED_LENGTH_SCCB
feature when the PV object link is first checked. So #248 CPUs is considered
valid, but when DIAG308_PV_START is called, it fails.
Let's simplify and use :
int offset_cpu = offsetof(ReadInfo, entries);
pv_max_cpus = (TARGET_PAGE_SIZE - offset_cpu) /sizeof(CPUEntry);
?
Thanks,
C.
