Re: [PATCH v2 8/8] KVM: arm64: Remove hyp_symbol_addr

From: Marc Zyngier <maz@kernel.org>
To: David Brazdil <dbrazdil@google.com>
Cc: kvmarm@lists.cs.columbia.edu,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 8/8] KVM: arm64: Remove hyp_symbol_addr
Date: Sat, 23 Jan 2021 13:54:47 +0000	[thread overview]
Message-ID: <87y2gjkbbs.wl-maz@kernel.org> (raw)
In-Reply-To: <20210105180541.65031-9-dbrazdil@google.com>

On Tue, 05 Jan 2021 18:05:41 +0000,
David Brazdil <dbrazdil@google.com> wrote:
> 
> Hyp code used the hyp_symbol_addr helper to force PC-relative addressing
> because absolute addressing results in kernel VAs due to the way hyp
> code is linked. This is not true anymore, so remove the helper and
> update all of its users.
> 
> Acked-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: David Brazdil <dbrazdil@google.com>
> ---
>  arch/arm64/include/asm/kvm_asm.h         | 26 ------------------------
>  arch/arm64/kvm/hyp/include/hyp/switch.h  |  4 ++--
>  arch/arm64/kvm/hyp/nvhe/hyp-smp.c        |  4 ++--
>  arch/arm64/kvm/hyp/nvhe/psci-relay.c     | 24 +++++++++++-----------
>  arch/arm64/kvm/hyp/vgic-v2-cpuif-proxy.c |  2 +-
>  5 files changed, 17 insertions(+), 43 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 8a33d83ea843..22d933e9b59e 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -199,32 +199,6 @@ extern void __vgic_v3_init_lrs(void);
>  
>  extern u32 __kvm_get_mdcr_el2(void);
>  
> -#if defined(GCC_VERSION) && GCC_VERSION < 50000
> -#define SYM_CONSTRAINT	"i"
> -#else
> -#define SYM_CONSTRAINT	"S"
> -#endif
> -
> -/*
> - * Obtain the PC-relative address of a kernel symbol
> - * s: symbol
> - *
> - * The goal of this macro is to return a symbol's address based on a
> - * PC-relative computation, as opposed to a loading the VA from a
> - * constant pool or something similar. This works well for HYP, as an
> - * absolute VA is guaranteed to be wrong. Only use this if trying to
> - * obtain the address of a symbol (i.e. not something you obtained by
> - * following a pointer).
> - */
> -#define hyp_symbol_addr(s)						\
> -	({								\
> -		typeof(s) *addr;					\
> -		asm("adrp	%0, %1\n"				\
> -		    "add	%0, %0, :lo12:%1\n"			\
> -		    : "=r" (addr) : SYM_CONSTRAINT (&s));		\
> -		addr;							\
> -	})
> -

This hunk is going to conflict in a fairly benign way with the
removal of the GCC workaround which I think Will queued for 5.12.
I'll work something out...

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.