It's erratum #1386 (see https://www.amd.com/system/files/TechDocs/56323-PUB_1.00.pdf https://www.amd.com/system/files/TechDocs/56323-PUB_1.00.pdf ): The XSAVES

It's erratum #1386 (see https://www.amd.com/system/files/TechDocs/56323-PUB_1.00.pdf https://www.amd.com/system/files/TechDocs/56323-PUB_1.00.pdf ): The XSAVES instruction may fail to save XMM registers to the provided state save area if all of the following are true: • All XMM registers were restored to the initialization value by the most recent XRSTORS instruction because the XSTATE_BV[SSE] bit was clear. • The state save area for the XMM registers does not contain the initialization state. • The value in the XMM registers match the initialization value when the XSAVES instruction is executed. • The MXCSR register has been modified to a value different from the initialization value since the most recent XRSTORS instruction.