Re: [PATCH 2/5] arm64: Handle UNDEF in the EL2 stub vectors
From: Robin Murphy <robin.murphy@arm.com>
Date: 2021-08-13 18:18:06
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On 2021-08-13 18:41, Marc Zyngier wrote:
On Fri, 13 Aug 2021 14:08:23 +0100, Robin Murphy [off-list ref] wrote:quoted
On 2021-08-12 20:02, Marc Zyngier wrote:quoted
As we want to handle the silly case where HVC has been disabled from EL3, augment our ability to handle exception at EL2. Check for unknown exceptions (usually UNDEF) coming from EL2, and treat them as a failing HVC call into the stubs. While this isn't great and obviously doesn't catter for the gigantic range of possible exceptions, it isn't any worse than what we have today. Just don't try and use it for anything else. Signed-off-by: Marc Zyngier <maz@kernel.org> --- arch/arm64/kernel/hyp-stub.S | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-)diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S index 43d212618834..026a34515b21 100644 --- a/arch/arm64/kernel/hyp-stub.S +++ b/arch/arm64/kernel/hyp-stub.S@@ -46,7 +46,16 @@ SYM_CODE_END(__hyp_stub_vectors) .align 11 SYM_CODE_START_LOCAL(elx_sync) - cmp x0, #HVC_SET_VECTORS + mrs x4, spsr_el2 + and x4, x4, #PSR_MODE_MASK + orr x4, x4, #1 + cmp x4, #PSR_MODE_EL2h + b.ne 0f + mrs x4, esr_el2 + eor x4, x4, #ESR_ELx_IL + cbz x4, el2_undefHmm, might it be neater to check ESR_EL2.ISS to see if we landed here for any reason *other* than a successfully-executed HVC?We absolutely could. However, the sixpence question (yes, that's the Brexit effect for you) is "what do you do with exceptions that are neither UNDEF now HVC?". We are taking a leap of faith by assuming that the only thing that will UNDEF at EL2 while the stubs are installed is HVC. If anything else occurs, I have no idea what to do with it. I guess we could always ignore it instead of treating it as a HVC (as it is done at the moment).
Right, I think that concern applies pretty much equally whichever way you slice it. "Any exception other than an unknown from EL2 must imply HVC" doesn't seem any less sketchy than "Any exception other than HVC implies something is horribly wrong and abandoning EL2 might be wise" to me, but it was primarily that the latter avoids having to faff with the SPSR as well. No big deal either way, just one of my "I reckon this could be shorter..." musings; it's been particularly Friday today :) Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel