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From: James Morse <james.morse@arm.com>
To: Marc Zyngier <maz@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Sami Tolvanen <samitolvanen@google.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	Julien Thierry <julien.thierry.kdev@gmail.com>
Subject: Re: [PATCH 0/3] KVM: arm64: Ask the compiler to __always_inline functions used by KVM at HYP
Date: Fri, 21 Feb 2020 14:57:48 +0000	[thread overview]
Message-ID: <228ef9d9-1ded-05ee-22e5-0158a0e47d82@arm.com> (raw)
In-Reply-To: <cb56f509ea0a4a9e1809af76f319daa2@kernel.org>

Hi Marc,

On 21/02/2020 12:55, Marc Zyngier wrote:
> On 2020-02-20 16:58, James Morse wrote:
>> It turns out KVM relies on the inline hint being honoured by the compiler
>> in quite a few more places than expected. Something about the Shadow Call
>> Stack support[0] causes the compiler to avoid inline-ing and to place
>> these functions outside the __hyp_text. This ruins KVM's day.
>>
>> Add the simon-says __always_inline annotation to all the static
>> inlines that KVM calls from HYP code.
>>
>> This series based on v5.6-rc2.
> 
> Many thanks for going through all this.
> 
> I'm happy to take it if Catalin or Will ack the arm64 patches.
> It case we decide to go the other way around:
> 
> Acked-by: Marc Zyngier <maz@kernel.org>
> 
> One thing I'd like to look into though is a compile-time check that
> nothing in the hyp_text section has a reference to a non-hyp_text
> symbol.

Heh, that hypothetical tool would choke on things like arch/arm64/kvm/hyp/tlb.c:
| static void __hyp_text __tlb_switch_to_guest_vhe(...)
| {

[...]

|	local_irq_save(cxt->flags);

which calls trace_hardirqs_off() ... which is absolutely fine because this only happens on
VHE.

To do it purely with the section information, you'd need to separate all the VHE code...
(maybe as a debug option that only runs when VHE is turned off?)


> We already have checks around non-init symbols pointing to init symbols,
> and I was wondering if we could reuse this for fun and profit...

I think objtool is the tool-of-the-future that can do this. You need something that
believes everything behind has_vhe() is unreachable...


Thanks,

James

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  reply	other threads:[~2020-02-21 14:58 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-20 16:58 [PATCH 0/3] KVM: arm64: Ask the compiler to __always_inline functions used by KVM at HYP James Morse
2020-02-20 16:58 ` [PATCH 1/3] KVM: arm64: Ask the compiler to __always_inline functions used " James Morse
2020-02-20 16:58 ` [PATCH 2/3] KVM: arm64: define our own swab32() to avoid a uapi static inline James Morse
2020-02-20 16:58 ` [PATCH 3/3] arm64: Ask the compiler to __always_inline functions used by KVM at HYP James Morse
2020-02-21 13:13   ` Will Deacon
2020-02-21 13:22     ` Ard Biesheuvel
2020-02-20 17:04 ` [PATCH 0/3] KVM: " Ard Biesheuvel
2020-02-20 17:33   ` James Morse
2020-02-20 17:35     ` Ard Biesheuvel
2020-02-21 12:55 ` Marc Zyngier
2020-02-21 14:57   ` James Morse [this message]
2020-02-21 16:38     ` Marc Zyngier
2020-02-24 13:22   ` Andrew Jones

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