Messages in this thread | | | Date | Thu, 10 Apr 2014 07:01:14 +0800 | From | Fengguang Wu <> | Subject | Re: [visorchipset] invalid opcode: 0000 [#1] PREEMPT SMP |
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CC the KVM people: it looks like a KVM problem that can be triggered by
qemu-system-x86_64 -cpu Haswell,+smep,+smap
On Thu, Apr 10, 2014 at 01:58:18AM +0800, Jet Chen wrote: > On 04/09/2014 10:44 PM, Romer, Benjamin M wrote: > > On Wed, 2014-04-09 at 02:38 +0800, Jet Chen wrote: > > > >> Hi Ben, > >> > >> I checked my <Intel 64 and IA-32 Architectures Software Developer's Manual> which published in Feb 2014. > >> Volume 2: Instruction Set Reference, A-Z: CPUID--CPU Identification > >> > > > > I agree completely, which is why I'm confused about KVM's behavior. If > > bit 31 was off, the code in our drivers that uses the vmcall instruction > > would not have been run, the kernel would not have tried to perform a > > vmcall, and not crashed with invalid op. > > > > If you look in the definition for the VMCALL instruction (Intel 64 and > > IA32 Architectures Software Developer's Manual, volume 3C pg.30-9) > > You'll see that a processor in VMX non-root operation should perform a > > vmexit. > > > >> Why this document not match what you said ? I am not experienced with VM, please correct me if I went for wrong document > >> > > > > According to VMWare's documentation (there is a page at > > http://kb.vmware.com./selfservice/microsites/search.do?cmd=displayKC&externalId=1009458 ) , as well as Microsoft's hypervisor spec (at http://www.microsoft.com/en-us/download/details.aspx?id=39289 ), this bit is used to indicate the CPU is running under virtualization. KVM is also setting this bit to indicate virtualization. I believe Xen uses it as well. > > > > > > My contention is, if KVM is going to set the ISVM bit, it needs to do a > > vmexit, and if it's not going to set the bit, then doing an invalid op > > is okay, but the current behavior is inconsistent. > > > > -- Ben > > > > Ben, > > Really thanks for your explanation. > Let me summary it up, please correct me where i am wrong. If it is really a KVM bug, we report it to KVM guys. > On a real CPU, ECX 31bit always be 0 as Intel documentation filed. > However, KVM, as a hypervisor, should emulate this bit of the virtual ECX register to 1 for guest OS to indicate it is running in a virtualization environment. > Problem is, KVM does set this bit to 1, but does an invalid op instead of emit a VMCALL. As a result, we get this dmesg error messages. > > Thanks, > -Jet
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