FAILED: patch "[PATCH] KVM: x86: SVM: Call x86_spec_ctrl_set_guest/host() with" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Sun, 12 Aug 2018 20:41:45 +0200
Subject: [PATCH] KVM: x86: SVM: Call x86_spec_ctrl_set_guest/host() with
interrupts disabled
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Mikhail reported the following lockdep splat:

WARNING: possible irq lock inversion dependency detected CPU 0/KVM/10284 just changed the state of lock:
000000000d538a88 (&st->lock){+...}, at:
speculative_store_bypass_update+0x10b/0x170

but this lock was taken by another, HARDIRQ-safe lock in the past:

(&(&sighand->siglock)->rlock){-.-.}

and interrupts could create inverse lock ordering between them.

Possible interrupt unsafe locking scenario:

    CPU0                    CPU1
    ----                    ----
   lock(&st->lock);
                           local_irq_disable();
                           lock(&(&sighand->siglock)->rlock);
                           lock(&st->lock);
    <Interrupt>
     lock(&(&sighand->siglock)->rlock);
     *** DEADLOCK ***

The code path which connects those locks is:

speculative_store_bypass_update()
ssb_prctl_set()
do_seccomp()
do_syscall_64()

In svm_vcpu_run() speculative_store_bypass_update() is called with interupts enabled via x86_virt_spec_ctrl_set_guest/host().

This is actually a false positive, because GIF=0 so interrupts are disabled even if IF=1; however, we can easily move the invocations of x86_virt_spec_ctrl_set_guest/host() into the interrupt disabled region to cure it, and it's a good idea to keep the GIF=0/IF=1 area as small and self-contained as possible.

index 73e27a98456f..6276140044d0 100644
@@ -5586,8 +5586,6 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 
 	clgi();
 
-	local_irq_enable();
-
 	/*
 	 * If this vCPU has touched SPEC_CTRL, restore the guest's value if
 	 * it's non-zero. Since vmentry is serialising on affected CPUs, there

@@ -5596,6 +5594,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 	 */
 	x86_spec_ctrl_set_guest(svm->spec_ctrl, svm->virt_spec_ctrl);
 
+	local_irq_enable();
+
 	asm volatile (
 		"push %%" _ASM_BP "; \n\t"
 		"mov %c[rbx](%[svm]), %%" _ASM_BX " \n\t"

@@ -5718,12 +5718,12 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 	if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
 		svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
 
-	x86_spec_ctrl_restore_host(svm->spec_ctrl, svm->virt_spec_ctrl);
-
 	reload_tss(vcpu);
 
 	local_irq_disable();
 
+	x86_spec_ctrl_restore_host(svm->spec_ctrl, svm->virt_spec_ctrl);
+
 	vcpu->arch.cr2 = svm->vmcb->save.cr2;
 	vcpu->arch.regs[VCPU_REGS_RAX] = svm->vmcb->save.rax;
 	vcpu->arch.regs[VCPU_REGS_RSP] = svm->vmcb->save.rsp;