Re: [Xen-devel] Weird altp2m behaviour when switching early to a new view

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Fri, Apr 13, 2018 at 8:44 AM, Razvan Cojocaru
<rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 04/11/2018 11:04 AM, Razvan Cojocaru wrote:
>> Debugging continues.
>
> Finally, the attached patch seems to get the display unstuck in my
> scenario, although for one guest I get:
>
> (XEN) d2v0 Unexpected vmexit: reason 49
> (XEN) domain_crash called from vmx.c:4120
> (XEN) Domain 2 (vcpu#0) crashed on cpu#1:
> (XEN) ----[ Xen-4.11-unstable  x86_64  debug=y   Not tainted ]----
> (XEN) CPU:    1
> (XEN) RIP:    0010:[<fffff96000842354>]
> (XEN) RFLAGS: 0000000000010246   CONTEXT: hvm guest (d2v0)
> (XEN) rax: fffff88003000000   rbx: fffff900c0083db0   rcx: 00000000aa55aa55
> (XEN) rdx: fffffa80041bdc41   rsi: fffff900c00c69a0   rdi: 0000000000000001
> (XEN) rbp: 0000000000000000   rsp: fffff88002ee9ef0   r8:  fffffa80041bdc40
> (XEN) r9:  fffff80001810e80   r10: fffffa800342aa70   r11: fffff88002ee9e80
> (XEN) r12: 0000000000000005   r13: 0000000000000001   r14: fffff900c00c08b0
> (XEN) r15: 0000000000000001   cr0: 0000000080050031   cr4: 00000000000406f8
> (XEN) cr3: 00000000ef771000   cr2: fffff900c00c8000
> (XEN) fsb: 00000000fffde000   gsb: fffff80001810d00   gss: 000007fffffdc000
> (XEN) ds: 002b   es: 002b   fs: 0053   gs: 002b   ss: 0018   cs: 0010
>
> i.e. EXIT_REASON_EPT_MISCONFIG - so not of the woods yet. I am hoping
> somebody more familiar with the code can point to a more elegant
> solution if one exists.

I dare say at this point you might just be that person :) I looked at
the patch, one issue with p2m_change_type_range in its current form is
that it's unclear how it would behave when the range contains remapped
gfns in an altp2m (either a page that remaps to this range, or a page
that remaps from the range). According to the current altp2m approach
I would say the altp2m views should probably just get completely reset
if there is such a remapping.

Tamas

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