Messages in this thread | | | Date | Fri, 13 Aug 2021 10:05:40 +0100 | From | Will Deacon <> | Subject | Re: [PATCH 3/5] arm64: Detect disabled HVC early |
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On Thu, Aug 12, 2021 at 08:02:11PM +0100, Marc Zyngier wrote: > Having HVC disabled from EL3 while the kernel is entered at EL2 > is a complete nightmare. > > We end-up taking an UNDEF at the worse possible moment (checking > for VHE) and even if we didn't, having KVM enabled would signify > the premature end of the kernel. > > Instead, try and detect this stupid case by issuing a HVC > for HVC_RESET_VECTORS, which does nothing when the stubs > are live. If we get HVC_STUB_ERR back, that's because the > UNDEF handler has kicked in. > > In this situation, close your eyes, block your nose, and gracefully > pretend we have booted at EL1. > > Reported-by: Rafał Miłecki <zajec5@gmail.com> > Signed-off-by: Marc Zyngier <maz@kernel.org> > --- > arch/arm64/kernel/head.S | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 9d5aa56a98cc..d6b2b05f5d3a 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -519,6 +519,28 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL) > msr vbar_el2, x0 > isb > > + // Check that HVC actually works... > + mov x0, #HVC_RESET_VECTORS > + hvc #0 > + > + mov_q x1, HVC_STUB_ERR > + cmp x0, x1 > + b.ne 0f > + > + /* > + * HVC is unusable, so pretend we actually booted at EL1. > + * Once we have left EL2, there will be no going back. > + */
This comment got me thinking...
.macro host_hvc0 mrs xzr, actlr_el1 .endm
then set HCR_EL2.TACR=1 while we still can and match the ISS against a constant in the handler. Too awful?
Will
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