[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2] x86/vpmu_intel: Fix hypervisor crash by masking PC bit in MSR_P6_EVNTSEL
>>> On 27.04.17 at 16:57, <boris.ostrovsky@xxxxxxxxxx> wrote: > On 04/27/2017 03:32 AM, Jan Beulich wrote: >>>>> On 26.04.17 at 20:50, <mohit.gambhir@xxxxxxxxxx> wrote: >>> On 04/26/2017 02:19 PM, Andrew Cooper wrote: >>>> On 26/04/17 19:11, Mohit Gambhir wrote: >>>>> Setting Pin Control (PC) bit (19) in MSR_P6_EVNTSEL results in a General >>>>> Protection Fault and thus results in a hypervisor crash. This patch fixes > the >>>>> crash by masking PC bit and returning an error in case any guest tries to > write >>>>> to it. >>>>> >>>>> Signed-off-by: Mohit Gambhir <mohit.gambhir@xxxxxxxxxx> >>>> Out of interest, which hardware has this been observed on? >>> I have tested this on two Intel Broadwell machines. >> Since by now all we have are indications that this is an erratum, >> this information belongs into the commit message. As it is written >> now, it means the bit can't be set on any hardware. If there are >> reasons beyond this erratum to uniformly disallow the bit to be >> set by guests, these should be named here too. After all the >> way you do the change, you now refuse values with the bit set >> everywhere. > > I don't think this is specific to Broadwell. I tried this on a Haswell > (model 60) and got a #GPF as well. > > If I understand what this bit does, it is pretty pointless in a guest. > It is only useful in some sort of embedded setup, where something is > hooked up to a particular pin on the board. So perhaps this is not an > erratum but rather a not fully documented feature, where if nothing is > connected to that pin this bit should not be set. > > Or maybe it is documented but I can't find anything on that. Kevin, Jun? > Either way, we should mask this bit. Sure, but: Refuse attempts to set it, or silently ignore such? Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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