On Tue, Feb 20, 2024 at 04:53:29PM +0100, Michal Privoznik wrote:
As of v9.8.0-rc1~7 we check whether two <memory/> devices don't overlap (since we allow setting where a <memory/> device should be mapped to). We do this pretty straightforward, by comparing start and end address of each <memory/> device combination. But since only the start address is given (an exposed in the XML), the end address is computed trivially as: start + mem->size * 1024 And for majority of memory device types this works. Except for NVDIMMs. For them the <memory/> device consists of two separate regions: 1) actual memory device, and 2) label. Label is where NVDIMM stores some additional information like namespaces partition and so on. But it's not mapped into the guest the same way as actual memory device. In fact, mem->size is a sum of both actual memory device and label sizes. And to make things a bit worse, both sizes are subject to alignment (either the alignsize value specified in XML, or system page size if not specified in XML). Therefore, to get the size of actual memory device we need to take mem->size and substract label size rounded up to alignment. If we don't do this we report there's an overlap between two NVDIMMs even when in reality there's none. Fixes: 3fd64fb0e236fc80ffa2cc977c0d471f11fc39bf Fixes: 91f9a9fb4fc0d34ed8d7a869de3d9f87687c3618 Resolves: https://issues.redhat.com/browse/RHEL-4452?focusedId=23805174#comment-23805174 Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx> --- src/conf/domain_validate.c | 50 ++++++++++++++++++++++++++++++++++++-- 1 file changed, 48 insertions(+), 2 deletions(-) diff --git a/src/conf/domain_validate.c b/src/conf/domain_validate.c index 46479f10f2..5a9398b545 100644 --- a/src/conf/domain_validate.c +++ b/src/conf/domain_validate.c @@ -2225,6 +2225,52 @@ virDomainHostdevDefValidate(const virDomainHostdevDef *hostdev) } +/** + * virDomainMemoryGetMappedSize: + * @mem: memory device definition + * + * For given memory device definition (@mem) calculate size mapped into + * the guest. This is usually mem->size, except for NVDIMM where its + * label is mapped elsewhere. + * + * Returns: Number of bytes a memory device takes when mapped into a + * guest. + */ +static unsigned long long +virDomainMemoryGetMappedSize(const virDomainMemoryDef *mem) +{ + unsigned long long ret = mem->size; + + if (mem->model == VIR_DOMAIN_MEMORY_MODEL_NVDIMM) { + unsigned long long alignsize = mem->source.nvdimm.alignsize; + unsigned long long labelsize = 0; + + /* For NVDIMM the situation is a bit more complicated. Firstly, + * its <label/> is not mapped as a part of memory device, so we + * must subtract label size from NVDIMM size. Secondly, label is + * also subject to alignment so we need to round it up before + * subtraction. */ + + if (alignsize == 0) { + long pagesize = virGetSystemPageSizeKB(); + + /* If no alignment is specified in the XML, fallback to + * system page size alignment. */ + if (pagesize > 0) + alignsize = pagesize;
I'm not very well versed in memory modules and architectures, but isn't this restricted a bit more, or rather isn't the QEMU default slightly different? The following two functions suggest it might be: qemuDomainGetMemorySizeAlignment qemuDomainGetMemoryModuleSizeAlignment
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