linux-kernel - Re: [PATCH v8 19/28] KVM: arm64: Support unaligned fixmap in the pKVM hyp

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Message-ID: <86ecpurq13.wl-maz@kernel.org>
Date: Wed, 19 Nov 2025 15:38:32 +0000
From: Marc Zyngier <maz@...nel.org>
To: Vincent Donnefort <vdonnefort@...gle.com>
Cc: rostedt@...dmis.org,
	mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com,
	linux-trace-kernel@...r.kernel.org,
	oliver.upton@...ux.dev,
	joey.gouly@....com,
	suzuki.poulose@....com,
	yuzenghui@...wei.com,
	kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	jstultz@...gle.com,
	qperret@...gle.com,
	will@...nel.org,
	aneesh.kumar@...nel.org,
	kernel-team@...roid.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 19/28] KVM: arm64: Support unaligned fixmap in the pKVM hyp

On Fri, 07 Nov 2025 09:38:31 +0000,
Vincent Donnefort <vdonnefort@...gle.com> wrote:
> 
> Return the fixmap VA with the page offset, instead of the page base
> address. This allows to use hyp_fixmap_map() seamlessly regardless of
> the address alignment.
> 
> Signed-off-by: Vincent Donnefort <vdonnefort@...gle.com>
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
> index ae8391baebc3..75014dc7d82e 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mm.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mm.c
> @@ -239,7 +239,7 @@ static void *fixmap_map_slot(struct hyp_fixmap_slot *slot, phys_addr_t phys)
>  	WRITE_ONCE(*ptep, pte);
>  	dsb(ishst);
>  
> -	return (void *)slot->addr;
> +	return (void *)slot->addr + offset_in_page(phys);
>  }
>  
>  void *hyp_fixmap_map(phys_addr_t phys)

This looks slightly odd. fixmap_map_slot() should return *a slot*, not
something in it. Can't hyp_fixmap_map() do that instead?

Thanks,

	M.

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