x86/xen: Make sure X2APIC_ENABLE bit of MSR_IA32_APICBASE is not set (31795b47) · Commits · 戴 / test

Commit ("x86/apic: Check x2apic early") tests X2APIC_ENABLE bit of MSR_IA32_APICBASE when CONFIG_X86_X2APIC is off and panics the kernel when this bit is set. Xen's PV guests will pass this MSR read to the hypervisor which will return its version of the MSR, where this bit might be set. Make sure we clear it before returning MSR value to the caller. Signed-off-by:

Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by:

David Vrabel <david.vrabel@citrix.com>

arch/x86/xen/enlighten.c

+18 −1

Original line number	Diff line number	Diff line
		@@ -1070,6 +1070,23 @@ static inline void xen_write_cr8(unsigned long val)
		BUG_ON(val);
		}
		#endif

		static u64 xen_read_msr_safe(unsigned int msr, int *err)
		{
		u64 val;

		val = native_read_msr_safe(msr, err);
		switch (msr) {
		case MSR_IA32_APICBASE:
		#ifdef CONFIG_X86_X2APIC
		if (!(cpuid_ecx(1) & (1 << (X86_FEATURE_X2APIC & 31))))
		#endif
		val &= ~X2APIC_ENABLE;
		break;
		}
		return val;
		}

		static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
		{
		int ret;
		@@ -1240,7 +1257,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {

		.wbinvd = native_wbinvd,

		.read_msr = native_read_msr_safe,
		.read_msr = xen_read_msr_safe,
		.write_msr = xen_write_msr_safe,

		.read_tsc = native_read_tsc,

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