x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only
On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA. In that case, KVM will fail to patch VMCALL instructions to VMMCALL as required on AMD processors. The failure mode is currently a divide-by-zero exception, which obviously is a KVM bug that has to be fixed. However, picking the right instruction between VMCALL and VMMCALL will be faster and will help if you cannot upgrade the hypervisor. Reported-by: Chris Webb <chris@arachsys.com> Tested-by: Chris Webb <chris@arachsys.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: x86@kernel.org Acked-by: Borislav Petkov <bp@suse.de> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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@ -202,6 +202,7 @@
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#define X86_FEATURE_DECODEASSISTS ( 8*32+12) /* AMD Decode Assists support */
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#define X86_FEATURE_DECODEASSISTS ( 8*32+12) /* AMD Decode Assists support */
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#define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */
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#define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */
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#define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */
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#define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */
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#define X86_FEATURE_VMMCALL ( 8*32+15) /* Prefer vmmcall to vmcall */
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/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
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/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
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@ -2,6 +2,7 @@
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#define _ASM_X86_KVM_PARA_H
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#define _ASM_X86_KVM_PARA_H
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#include <asm/processor.h>
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#include <asm/processor.h>
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#include <asm/alternative.h>
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#include <uapi/asm/kvm_para.h>
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#include <uapi/asm/kvm_para.h>
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extern void kvmclock_init(void);
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extern void kvmclock_init(void);
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@ -16,10 +17,15 @@ static inline bool kvm_check_and_clear_guest_paused(void)
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}
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}
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#endif /* CONFIG_KVM_GUEST */
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#endif /* CONFIG_KVM_GUEST */
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/* This instruction is vmcall. On non-VT architectures, it will generate a
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#ifdef CONFIG_DEBUG_RODATA
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* trap that we will then rewrite to the appropriate instruction.
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#define KVM_HYPERCALL \
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ALTERNATIVE(".byte 0x0f,0x01,0xc1", ".byte 0x0f,0x01,0xd9", X86_FEATURE_VMMCALL)
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#else
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/* On AMD processors, vmcall will generate a trap that we will
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* then rewrite to the appropriate instruction.
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*/
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*/
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#define KVM_HYPERCALL ".byte 0x0f,0x01,0xc1"
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#define KVM_HYPERCALL ".byte 0x0f,0x01,0xc1"
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#endif
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/* For KVM hypercalls, a three-byte sequence of either the vmcall or the vmmcall
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/* For KVM hypercalls, a three-byte sequence of either the vmcall or the vmmcall
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* instruction. The hypervisor may replace it with something else but only the
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* instruction. The hypervisor may replace it with something else but only the
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@ -525,6 +525,13 @@ static void early_init_amd(struct cpuinfo_x86 *c)
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}
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}
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#endif
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#endif
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/*
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* This is only needed to tell the kernel whether to use VMCALL
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* and VMMCALL. VMMCALL is never executed except under virt, so
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* we can set it unconditionally.
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*/
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set_cpu_cap(c, X86_FEATURE_VMMCALL);
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/* F16h erratum 793, CVE-2013-6885 */
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/* F16h erratum 793, CVE-2013-6885 */
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if (c->x86 == 0x16 && c->x86_model <= 0xf)
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if (c->x86 == 0x16 && c->x86_model <= 0xf)
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msr_set_bit(MSR_AMD64_LS_CFG, 15);
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msr_set_bit(MSR_AMD64_LS_CFG, 15);
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