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Wed, 15 Jan 2025 18:39:42 +0000 Message-ID: Date: Wed, 15 Jan 2025 10:39:40 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/fpu: Fix the os panic issue caused by the XGETBV instruction To: Tony W Wang-oc , , , , , , , , , , , CC: , , , Lyle Li References: <20250102075419.2559-1-TonyWWang-oc@zhaoxin.com> Content-Language: en-US From: "Chang S. 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However, in some > places where xfeatures_in_use is called, there is no check to see if the > processor supports this feature, leading to the execution of the XGETBV > XCR1 instruction on processors that do not support this feature, > triggering a #GP exception, and ultimately causing an OS panic. I doubt this is a real issue. An XFD implementation without XGETBV1 is considerably broken; every AMX system includes XGETBV1. Similarly, as far as I can see, PKU implementations also include XGETBV1. QEMU's CPU feature list [1] seems consistent with this. Maybe a wild clearcpuid use may clear off the XGETBV1 flag. Adding this dependency to the table would make the relationship explicit: static const struct cpuid_dep cpuid_deps[] = { ... + { X86_FEATURE_PKU, X86_FEATURE_XGETBV1 }, {} }; Note that XFD is already listed as dependent on XGETBV1. But I doubt the kernel needs to be resilient to deliberately misconfigured or crazy virtual machine setups. Thanks, Chang [1] https://github.com/qemu/qemu/blob/master/target/i386/cpu.c