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Re: [PATCH 2/5] qemu_validate.c: add pSeries NVDIMM size alignment validation



On 7/30/20 9:48 PM, Daniel Henrique Barboza wrote:
The existing auto-align behavior for pSeries has the idea to
alleviate user configuration of the NVDIMM size, given that the
alignment calculation is not trivial to do (256MiB alignment
of mem->size - mem->label_size value, a.k.a guest area). We
align mem->size down to avoid end of file problems.

The end result is not ideal though. We do not touch the domain
XML, meaning that the XML can report a NVDIMM size 255MiB smaller
than the actual size the guest is seeing. It also adds one more
thing to consider in case the guest is reporting less memory
than declared, since the auto-align is transparent to the
user.

Following Andrea's suggestion in [1], let's instead do an
size alignment validation. If the NVDIMM is unaligned, error out
and suggest a rounded up value. This can be bothersome to users,
but will bring consistency of NVDIMM size between the domain XML
and the guest.

This approach will force existing non-running pSeries guests to
readjust the NVDIMM value in their XMLs, if necessary. No changes
were made for x86 NVDIMM support.

[1] https://www.redhat.com/archives/libvir-list/2020-July/msg01471.html

Suggested-by: Andrea Bolognani <abologna redhat com>
Signed-off-by: Daniel Henrique Barboza <danielhb413 gmail com>
---
  src/qemu/qemu_validate.c                      | 43 ++++++++++++++++---
  ...ory-hotplug-nvdimm-ppc64.ppc64-latest.args |  2 +-
  .../memory-hotplug-nvdimm-ppc64.xml           |  2 +-
  .../memory-hotplug-nvdimm-ppc64.xml           |  2 +-
  4 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/src/qemu/qemu_validate.c b/src/qemu/qemu_validate.c
index 488f258d00..241139e268 100644
--- a/src/qemu/qemu_validate.c
+++ b/src/qemu/qemu_validate.c
@@ -4012,15 +4012,46 @@ qemuValidateDomainDeviceDefHub(virDomainHubDefPtr hub,
  }
+static unsigned long long
+qemuValidateGetNVDIMMAlignedSizePseries(virDomainMemoryDefPtr mem,
+                                        const virDomainDef *def)
+{
+    unsigned long long ppc64AlignSize =
+        qemuDomainGetMemorySizeAlignment((virDomainDefPtr)def);

Ouch. This is not nice. We need a trivial patch that makes qemuDomainGetMemorySizeAlignment() accept a const virDomainDef. I'm placing it at the beginning before 1/5.

+    unsigned long long guestArea = mem->size - mem->labelsize;
+
+    // NVDIMM is already aligned

We're old style, we use c89 style of comments :-)

+    if (guestArea % ppc64AlignSize == 0)
+        return mem->size;
+
+    // Suggested aligned size is rounded up
+    guestArea = (guestArea/ppc64AlignSize + 1) * ppc64AlignSize;
+    return guestArea + mem->labelsize;
+}

Michal


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