linux-kernel - Re: [PATCH v2 1/9] KVM: arm64: Handle huge mappings for np-guest CMOs

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Message-ID: <Z-6aEOQlbfh_q2Mz@google.com>
Date: Thu, 3 Apr 2025 14:24:16 +0000
From: Quentin Perret <qperret@...gle.com>
To: Vincent Donnefort <vdonnefort@...gle.com>
Cc: maz@...nel.org, oliver.upton@...ux.dev, joey.gouly@....com,
	suzuki.poulose@....com, yuzenghui@...wei.com,
	catalin.marinas@....com, will@...nel.org,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v2 1/9] KVM: arm64: Handle huge mappings for np-guest CMOs

On Thursday 06 Mar 2025 at 11:00:30 (+0000), Vincent Donnefort wrote:
> clean_dcache_guest_page() and invalidate_icache_guest_page() accept a
> size as an argument. But they also rely on fixmap, which can only map a
> single PAGE_SIZE page.
> 
> With the upcoming stage-2 huge mappings for pKVM np-guests, those
> callbacks will get size > PAGE_SIZE. Loop the CMOs on PAGE_SIZE basis
> until the whole range is done.
> 
> Signed-off-by: Vincent Donnefort <vdonnefort@...gle.com>
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index 19c3c631708c..63968c7740c3 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -219,14 +219,30 @@ static void guest_s2_put_page(void *addr)
>  
>  static void clean_dcache_guest_page(void *va, size_t size)
>  {
> -	__clean_dcache_guest_page(hyp_fixmap_map(__hyp_pa(va)), size);
> -	hyp_fixmap_unmap();
> +	if (WARN_ON(!PAGE_ALIGNED(size)))
> +		return;

Nit: it doesn't really matter since WARN_ON() is fatal, but that return
looks a bit weird -- we really shouldn't return without actually do the
CMOs. So maybe just WARN_ON() and not bailing out would be clearer.

Either way the patch works, so:

Reviewed-by: Quentin Perret <qperret@...gle.com>


> +
> +	while (size) {
> +		__clean_dcache_guest_page(hyp_fixmap_map(__hyp_pa(va)),
> +					  PAGE_SIZE);
> +		hyp_fixmap_unmap();
> +		va += PAGE_SIZE;
> +		size -= PAGE_SIZE;
> +	}
>  }
>  
>  static void invalidate_icache_guest_page(void *va, size_t size)
>  {
> -	__invalidate_icache_guest_page(hyp_fixmap_map(__hyp_pa(va)), size);
> -	hyp_fixmap_unmap();
> +	if (WARN_ON(!PAGE_ALIGNED(size)))
> +		return;
> +
> +	while (size) {
> +		__invalidate_icache_guest_page(hyp_fixmap_map(__hyp_pa(va)),
> +					       PAGE_SIZE);
> +		hyp_fixmap_unmap();
> +		va += PAGE_SIZE;
> +		size -= PAGE_SIZE;
> +	}
>  }
>  
>  int kvm_guest_prepare_stage2(struct pkvm_hyp_vm *vm, void *pgd)
> -- 
> 2.48.1.711.g2feabab25a-goog
>