Re: [RFC v2 0/5] arm64: kvm: reset hyp context for kexec

[AKASHI Takahiro]

Marc,

On 03/30/2015 05:54 PM, AKASHI Takahiro wrote:
> On 03/30/2015 04:16 PM, Marc Zyngier wrote:
> > On Mon, 30 Mar 2015 02:39:53 +0100
> > AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> wrote:
> >
> > > On 03/28/2015 02:40 AM, Kyle McMartin wrote:
> > > > On Fri, Mar 27, 2015 at 03:37:04PM +0000, Marc Zyngier wrote:
> > > > > > [  236.260863] Kernel panic - not syncing: HYP panic:
> > > > > > [  236.260863] PS:600003c9 PC:000003ffffff0830 ESR:0000000096000006
> > > > >
> > > > > It would be interesting if you could find out what you have at offset
> > > > > 0x830 of hyp-init.o (the stack trace is for EL1, and is not going to
> > > > > help much).
> > > >
> > > > Given the alignment, i'm going to assume i'm looking at the right thing:
> > > >
> > > > 0000000000000820 <__kvm_hyp_reset>:
> > > >        820:       d51c2000        msr     ttbr0_el2, x0
> > > >        824:       d5033fdf        isb
> > > >        828:       d50c871f        tlbi    alle2
> > > >        82c:       d5033f9f        dsb     sy
> > > >        830:       10000060        adr     x0, 83c <__kvm_hyp_reset+0x1c>
> > > >        834:       b3403c01        bfxil   x1, x0, #0, #16
> > > >        838:       d61f0020        br      x1
> > > >        83c:       d53c1000        mrs     x0, sctlr_el2
> > > >
> > > > but it seems fairly implausible to be trapping on ADR x0, 1f...
> > >
> > >
> > > I've never seen this panic on fast model...
> > >
> > > ESR shows that
> > >     - Exception class: Data abort taken without a change in Exception level
> > >     - Data fault status code: Translation fault at EL2
> > >
> > > and FAR seems not to be a proper address.
> >
> > ... which is consistent with what we're seeing here (data fault on
> > something that doesn't generate a load/store). I'm pretty sure the
> > page tables are screwed.
> >
> > Have you tested it with 64k pages?
>
> Hmm... It seems that I was able to reproduce the problem if 64k pages enabled.

The entry address in trampoline code calc'ed by kvm_virt_to_trampoline(__kvm_hyp_reset)
seems to be wrong due to improper page-alignment in hyp-init.S.
The following patch fixed this problem, at least, in my environment(fast model).
(I don't know why it's PAGE_SHIFT - 1, not PAGE_SHIFT.)

>diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
>index d212990..45b8d98 100644
>--- a/arch/arm64/kvm/hyp-init.S
>+++ b/arch/arm64/kvm/hyp-init.S
>@@ -24,7 +24,7 @@
>        .text
>        .pushsection    .hyp.idmap.text, "ax"
>
>-       .align  11
>+       .align  (PAGE_SHIFT - 1)
>
> ENTRY(__kvm_hyp_init)
>        ventry  __invalid               // Synchronous EL2t


After applying this patch, I got another problem with kexec-tools on 64k page kernel,
but I've already modified kexec-tools.


Thanks,
-Takahiro AKASHI


> -Takahiro AKASHI
>
> > Thanks,
> >
> >          M.
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