Re: Flask vs paging mempool - Was: [xen-unstable test] 174809: regressions - trouble: broken/fail/pass

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Fri, Nov 18, 2022 at 12:22 PM Andrew Cooper
<Andrew.Cooper3@xxxxxxxxxx> wrote:
>
> On 18/11/2022 14:39, Roger Pau Monne wrote:
> > Nov 18 01:55:11.753936 (XEN) arch/x86/mm/hap/hap.c:304: d1 failed to 
> > allocate from HAP pool
> > Nov 18 01:55:18.633799 (XEN) Failed to shatter gfn 7ed37: -12
> > Nov 18 01:55:18.633866 (XEN) d1v0 EPT violation 0x19c (--x/rw-) gpa 
> > 0x0000007ed373a1 mfn 0x33ed37 type 0
> > Nov 18 01:55:18.645790 (XEN) d1v0 Walking EPT tables for GFN 7ed37:
> > Nov 18 01:55:18.645850 (XEN) d1v0  epte 9c0000047eba3107
> > Nov 18 01:55:18.645893 (XEN) d1v0  epte 9c000003000003f3
> > Nov 18 01:55:18.645935 (XEN) d1v0  --- GLA 0x7ed373a1
> > Nov 18 01:55:18.657783 (XEN) domain_crash called from 
> > arch/x86/hvm/vmx/vmx.c:3758
> > Nov 18 01:55:18.657844 (XEN) Domain 1 (vcpu#0) crashed on cpu#8:
> > Nov 18 01:55:18.669781 (XEN) ----[ Xen-4.17-rc  x86_64  debug=y  Not 
> > tainted ]----
> > Nov 18 01:55:18.669843 (XEN) CPU:    8
> > Nov 18 01:55:18.669884 (XEN) RIP:    0020:[<000000007ed373a1>]
> > Nov 18 01:55:18.681711 (XEN) RFLAGS: 0000000000010002   CONTEXT: hvm guest 
> > (d1v0)
> > Nov 18 01:55:18.681772 (XEN) rax: 000000007ed373a1   rbx: 000000007ed3726c  
> >  rcx: 0000000000000000
> > Nov 18 01:55:18.693713 (XEN) rdx: 000000007ed2e610   rsi: 0000000000008e38  
> >  rdi: 000000007ed37448
> > Nov 18 01:55:18.693775 (XEN) rbp: 0000000001b410a0   rsp: 0000000000320880  
> >  r8:  0000000000000000
> > Nov 18 01:55:18.705725 (XEN) r9:  0000000000000000   r10: 0000000000000000  
> >  r11: 0000000000000000
> > Nov 18 01:55:18.717733 (XEN) r12: 0000000000000000   r13: 0000000000000000  
> >  r14: 0000000000000000
> > Nov 18 01:55:18.717794 (XEN) r15: 0000000000000000   cr0: 0000000000000011  
> >  cr4: 0000000000000000
> > Nov 18 01:55:18.729713 (XEN) cr3: 0000000000400000   cr2: 0000000000000000
> > Nov 18 01:55:18.729771 (XEN) fsb: 0000000000000000   gsb: 0000000000000000  
> >  gss: 0000000000000002
> > Nov 18 01:55:18.741711 (XEN) ds: 0028   es: 0028   fs: 0000   gs: 0000   
> > ss: 0028   cs: 0020
> >
> > It seems to be related to the paging pool adding Andrew and Henry so
> > that he is aware.
>
> Summary of what I've just given on IRC/Matrix.
>
> This crash is caused by two things.  First
>
>   (XEN) FLASK: Denying unknown domctl: 86.
>
> because I completely forgot to wire up Flask for the new hypercalls.
> But so did the original XSA-409 fix (as SECCLASS_SHADOW is behind
> CONFIG_X86), so I don't feel quite as bad about this.

Broken for ARM, but not for x86, right?

I think SECCLASS_SHADOW is available in the policy bits - it's just
whether or not the hook functions are available?

> And second because libxl ignores the error it gets back, and blindly
> continues onward.  Anthony has posted "libs/light: Propagate
> libxl__arch_domain_create() return code" to fix the libxl half of the
> bug, and I posted a second libxl bugfix to fix an error message.  Both
> are very simple.
>
>
> For Flask, we need new access vectors because this is a common
> hypercall, but I'm unsure how to interlink it with x86's shadow
> control.  This will require a bit of pondering, but it is probably
> easier to just leave them unlinked.

It sort of seems like it could go under domain2 since domain/domain2
have most of the memory stuff, but it is non-PV.  shadow has its own
set of hooks.  It could go in hvm which already has some memory stuff.

> Flask is listed as experimental which means it doesn't technically
> matter if we break it, but it is used by OpenXT so not fixing it for
> 4.17 would be rather rude.

It's definitely nicer to have functional Flask in the release.  OpenXT
can use a backport if necessary, so it doesn't need to be a release
blocker.  Having said that, Flask is a nice feature of Xen, so it
would be good to have it functioning in 4.17.

Regards,
Jason