Re: [BUG] kvm crashes in 2.6.28-rc6-00007-ged31348

[Avi Kivity <avi@redhat.com>]

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Avi Kivity wrote:
> Steven Rostedt wrote:
>> The following must be available without recursion for the function
>> tracer to work:
>>
>>   local_irq_save/restore
>>   smp_processor_id
>>   preempt_enable/disable_notrace
>>   atomic_inc/dec
>>   
>
> In arch/x86/kvm/svm.c, function svm_vcpu_run(), everything between the 
> vmrun instruction and the call to load_host_msrs() is executed without 
> a live pda, so no smp_processor_id().  Could easily be fixed by 
> rearranging things.
>
>

Luis, please try the attached patch.


-- 
error compiling committee.c: too many arguments to function


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diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 1452851..c10857d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -920,13 +920,6 @@ static int svm_get_irq(struct kvm_vcpu *vcpu)
 	return -1;
 }
 
-static void load_host_msrs(struct kvm_vcpu *vcpu)
-{
-#ifdef CONFIG_X86_64
-	wrmsrl(MSR_GS_BASE, to_svm(vcpu)->host_gs_base);
-#endif
-}
-
 static void save_host_msrs(struct kvm_vcpu *vcpu)
 {
 #ifdef CONFIG_X86_64
@@ -1798,10 +1791,26 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 		"mov %%r14, %c[r14](%[svm]) \n\t"
 		"mov %%r15, %c[r15](%[svm]) \n\t"
 #endif
-		"pop %%"R"bp"
+		"pop %%"R"bp \n\t"
+		/* Reload PDA early so ftrace can work */
+		"mov %[fs], %%fs \n\t"
+		"mov %[gs], %%gs \n\t"
+#ifdef CONFIG_X86_64
+		"mov %c[gsbase](%[svm]), %%edi \n\t"
+		"mov %c[gsbase]+4(%[svm]), %%edx \n\t"
+		"mov %[msr_gs_base], %%ecx \n\t"
+		"xchg %%rax, %%rdi \n\t"
+		"wrmsr \n\t"
+		"xchg %%rax, %%rdi \n\t"
+#endif
 		:
 		: [svm]"a"(svm),
 		  [vmcb]"i"(offsetof(struct vcpu_svm, vmcb_pa)),
+		  [fs]"g"(fs_selector), [gs]"g"(gs_selector),
+#ifdef CONFIG_X86_64
+		  [gsbase]"i"(offsetof(struct vcpu_svm, host_gs_base)),
+		  [msr_gs_base]"i"(MSR_GS_BASE),
+#endif
 		  [rbx]"i"(offsetof(struct vcpu_svm, vcpu.arch.regs[VCPU_REGS_RBX])),
 		  [rcx]"i"(offsetof(struct vcpu_svm, vcpu.arch.regs[VCPU_REGS_RCX])),
 		  [rdx]"i"(offsetof(struct vcpu_svm, vcpu.arch.regs[VCPU_REGS_RDX])),
@@ -1837,10 +1846,7 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	write_dr7(svm->host_dr7);
 	kvm_write_cr2(svm->host_cr2);
 
-	kvm_load_fs(fs_selector);
-	kvm_load_gs(gs_selector);
 	kvm_load_ldt(ldt_selector);
-	load_host_msrs(vcpu);
 
 	reload_tss(vcpu);