Re: [RFH]: AMD SVM #PF error code with P and RSVD bit....

[Mukesh Rathor <mukesh.rathor@oracle.com>]

On Tue, 17 Jun 2014 14:32:44 +0100
Andrew Cooper <andrew.cooper3@citrix.com> wrote:

> On 17/06/14 08:01, Jan Beulich wrote:
> >>>> On 17.06.14 at 00:44, <mukesh.rathor@oracle.com> wrote:
> >> On Mon, 16 Jun 2014 10:24:15 +0100
> >> "Jan Beulich" <JBeulich@suse.com> wrote:
> >>
> >>>>>> On 14.06.14 at 03:03, <mukesh.rathor@oracle.com> wrote:
> >>>> I am trying to debug this triple fault bringing up PVH linux
> >>>> domU on AMD.
> >>>>
> >>>> Instruction:
> >>>> ffffffff81d2d976: 8:dmi_scan_machine+b7          mov (%r12),
> >>>> %rax r12: ffffffffff46e000
> >>>>
> >>>> This first causes #PF:
> >>>> (XEN) exitcode = 0x4e exitintinfo = 0
> >>>> (XEN) exitinfo1 = 0x9 exitinfo2 = 0xffffffffff46e000 
> >>>>
> >>>> erro_code == 0x9 => RSVD bit set. according to the APM:
> >>>>
> >>>>    RSV—Bit 3. If this bit is set to 1, the page fault is a result
> >>>>    of the processor reading a 1 from a reserved field within a
> >>>>    page-translation-table entry. This type of page fault occurs
> >>>> only when CR4.PSE=1 or CR4.PAE=1.
> >>>>
> >>>> My CR4 == 0x0000000000000060 == PAE MCE (Full vmcb below). 
> >>>> However, all PTEs seem OK, all NPT entries seem OK too.
> >>>>
> >>>> PTE entries (l4 thru L1):
> >>>>
> >>>> 0000000001c16067 0000000001c18067 0000000001e8d067
> >>>> 80000000000f0463 
> >>> EFER.NX is clear, and hence the NX bit on the L1 entry is wrong.
> >> Ah, interesting, I didn't realize it would complain about NX
> >> during load/store.
> >>
> >> BTW on:
> >>
> >> Intel:
> >>     Guest EFER = 0x0000000000000000
> >>
> >>     Ptes:
> >>        0000000001c16067 0000000001c18067 0000000001e8d067
> >> 80000000000f0463
> >>
> >> L1 has XD set. Maybe Intel just ignores the bit if EFER.NX is 0!
> > Which would be a bug imo.
> 
> Intel Manual vol 3, 4.4.2 (32bit PAE) and 4.5 (64bit) states that
> EFER.NXE = 0 and L1.P = 1 causes the L1.NX to be reserved, and must
> be 0.
> 
> I would expect this to fail with with a #PF indicating RSVD on Intel
> as well as AMD.
> 
> I wonder whether there are some interaction issues with the non-root
> paging mode?

Hmm.. can't think of any, appears to be a processor issue.


[Adding Intel folks]

Hi Intel folks,

Can you please confirm if this is processor issue, and if yes, is
there need to open bug, and if yes, how?

thanks
Mukesh




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