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amd64: do not enable PKRU if user disabled saving PKRU register in xsave mask
This is done by reverting CR4_PKE bit, because we perform %CR4 initialization in initializecpu(), and the function is called before xsave_mask is read. To not redo the whole early initialization sequence for the corner case, this should be good enough. Reported by: jhb Reviewed by: jhb, markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D38219
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@ -372,6 +372,7 @@ void
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fpuinit(void)
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{
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register_t saveintr;
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uint64_t cr4;
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u_int mxcsr;
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u_short control;
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@ -379,7 +380,22 @@ fpuinit(void)
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fpuinit_bsp1();
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if (use_xsave) {
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load_cr4(rcr4() | CR4_XSAVE);
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cr4 = rcr4();
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/*
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* Revert enablement of PKRU if user disabled its
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* saving on context switches by clearing the bit in
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* the xsave mask. Also redundantly clear the bit in
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* cpu_stdext_feature2 to prevent pmap from ever
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* trying to set the page table bits.
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*/
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if ((cpu_stdext_feature2 & CPUID_STDEXT2_PKU) != 0 &&
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(xsave_mask & XFEATURE_ENABLED_PKRU) == 0) {
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cr4 &= ~CR4_PKE;
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cpu_stdext_feature2 &= ~CPUID_STDEXT2_PKU;
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}
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load_cr4(cr4 | CR4_XSAVE);
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load_xcr(XCR0, xsave_mask);
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}
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