linux-kernel - Re: [PATCH 2/2] KVM: arm64: Minor optimization of range_is

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Date:   Thu, 29 Jul 2021 18:00:23 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     David Brazdil <dbrazdil@...gle.com>
Cc:     kvmarm@...ts.cs.columbia.edu, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: arm64: Minor optimization of range_is_memory

On Wednesday 28 Jul 2021 at 15:32:32 (+0000), David Brazdil wrote:
> Currently range_is_memory finds the corresponding struct memblock_region
> for both the lower and upper bounds of the given address range with two
> rounds of binary search, and then checks that the two memblocks are the
> same. Simplify this by only doing binary search on the lower bound and
> then checking that the upper bound is in the same memblock.
> 
> Signed-off-by: David Brazdil <dbrazdil@...gle.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index a6ce991b1467..37d73af69634 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -189,13 +189,18 @@ static bool find_mem_range(phys_addr_t addr, struct kvm_mem_range *range)
>  	return false;
>  }
>  
> +static bool is_in_mem_range(phys_addr_t addr, struct kvm_mem_range *range)
> +{

Nit: addr@ could be u64 for consistency -- struct kvm_mem_range holds
IPAs in general.

> +	return range->start <= addr && addr < range->end;
> +}
> +
>  static bool range_is_memory(u64 start, u64 end)
>  {
> -	struct kvm_mem_range r1, r2;
> +	struct kvm_mem_range r;
>  
> -	if (!find_mem_range(start, &r1) || !find_mem_range(end - 1, &r2))
> +	if (!find_mem_range(start, &r))
>  		return false;
> -	if (r1.start != r2.start)
> +	if (!is_in_mem_range(end - 1, &r))
>  		return false;
>  
>  	return true;

Nit: maybe drop the second if and simplify to:

	return is_in_mem_range(end - 1, &r);

With that:

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

Thanks,
Quentin