* Ingo Molnar <[EMAIL PROTECTED]> wrote:
> * Avi Kivity <[EMAIL PROTECTED]> wrote:
>
> > >NOTE: this is not a worry for upstream kernel, it is caused by
> > >PREEMPT_RT scheduling in previously atomic APIs like kunmap(). But
> > >KVM used to work pretty nicely in -rt and this problem got introduced
> > >fairly recently, related to some big-page changes IIRC.
> >
> > This is not a recent change. The x86 emulator is fetching an
> > instruction or a memory operand.
>
> well, the fact that it's somehow ending up in highmem and thus the
> kmap becomes nontrivial could be a recent change maybe?
i have worked the problem around via the change below. This affects
32-bit hosts only, and only on CONFIG_PREEMPT_RT.
with this and the other two patches kvm/vmx works on 32-bit -rt hosts.
Ingo
Index: linux/drivers/kvm/kvm_main.c
===================================================================
--- linux.orig/drivers/kvm/kvm_main.c
+++ linux/drivers/kvm/kvm_main.c
@@ -628,8 +628,12 @@ raced:
memset(new.phys_mem, 0, npages * sizeof(struct page *));
for (i = 0; i < npages; ++i) {
+#ifdef CONFIG_PREEMPT_RT
+ new.phys_mem[i] = alloc_page(GFP_USER | __GFP_ZERO);
+#else
new.phys_mem[i] = alloc_page(GFP_HIGHUSER
| __GFP_ZERO);
+#endif
if (!new.phys_mem[i])
goto out_free;
}
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