On 12/20/17 19:26 -0200, Eduardo Habkost wrote: > On Tue, Dec 19, 2017 at 10:54:16AM +0800, Haozhong Zhang wrote: > > On 12/18/17 16:36 -0200, Eduardo Habkost wrote: > > > On Tue, Dec 12, 2017 at 04:35:24PM +0800, Haozhong Zhang wrote: > > > > Intel VMX cannot intercept guest clwb and clflushopt. When clwb and > > > > clflushopt are not exposed in guest cpuid, clwb and clflushopt > > > > instructions in this test case can still succeed without #UD on the > > > > host CPU which has clwb and clflushopt support, though failures with > > > > UD are expected. > > > > > > > > In order to avoid false alarms in such cases, introduce the following > > > > two arguments "has_clwb" and "has_clflushopt" to allow users to > > > > specify whether clwb and clflushopt are supported on the host CPU. > > > > > > > > Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx> > > > > --- > > > > x86/memory.c | 29 +++++++++++++++++++++++++++-- > > > > 1 file changed, 27 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/x86/memory.c b/x86/memory.c > > > > index cd1eb46..03ff7d3 100644 > > > > --- a/x86/memory.c > > > > +++ b/x86/memory.c > > > > @@ -23,10 +23,29 @@ static void handle_ud(struct ex_regs *regs) > > > > regs->rip += isize; > > > > } > > > > > > > > +/* > > > > + * Intel VMX cannot intercept guest clwb and clflushopt. When clwb and > > > > + * clflushopt are not exposed in guest cpuid, clwb and clflushopt > > > > + * instructions in this test case can still succeed without #UD on > > > > + * the host CPU which has clwb and clflushopt support. In order to avoid > > > > + * false alarms in such cases, introduce the following two arguments > > > > + * to allow users to specify whether clwb and clflushopt are supported on > > > > + * the host CPU: > > > > + * - has_clwb: indicates clwb is supported on the host CPU > > > > + * - has_clflushopt: indicates clflushopt is supported on the host CPU > > > > + */ > > > > > > Why not simply use "-cpu host" to make sure the guest CPUID flags > > > match host CPUID? > > > > > > > Can I understand that testing these two cases with host/guest CPUID > > mismatch (specially clwb and clflushopt flags) is invalid? If yes, > > please ignore this patch. > > I wouldn't say it's invalid to test what happens when the host > and guest CPUID don't match. The question is: is it useful to do > so? Are we testing different code paths when we do that? > No, VMX cannot intercept guest clwb and clflushopt, so no KVM code path is involved when guest executes those two instructions. > The inability to trigger #UD if the host CPUID includes the flag > sounds like a bug/limitation we would like to get rid of as soon > as hardware allow us to, and not a feature we need to test for. > It's more the inability of VMX, which cannot intercept clwb and clflushopt. > What's the right way to ensure memory.flat is always tested using > "-cpu host"? > I think so, at least '-cpu host' can mitigate the hardware inability. Haozhong
