linux-kernel - Re: [PATCH] KVM: arm/arm64: release kvm->mmu

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Date:   Thu, 7 May 2020 12:01:28 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     giangyi@...zon.com, maz@...nel.org
Cc:     james.morse@....com, julien.thierry.kdev@...il.com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm/arm64: release kvm->mmu_lock in loop to prevent
 starvation

On 04/15/2020 09:42 AM, Jiang Yi wrote:
> Do cond_resched_lock() in stage2_flush_memslot() like what is done in
> unmap_stage2_range() and other places holding mmu_lock while processing
> a possibly large range of memory.
> 
> Signed-off-by: Jiang Yi <giangyi@...zon.com>
> ---
>   virt/kvm/arm/mmu.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index e3b9ee268823..7315af2c52f8 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -417,16 +417,19 @@ static void stage2_flush_memslot(struct kvm *kvm,
>   	phys_addr_t next;
>   	pgd_t *pgd;
>   
>   	pgd = kvm->arch.pgd + stage2_pgd_index(kvm, addr);
>   	do {
>   		next = stage2_pgd_addr_end(kvm, addr, end);
>   		if (!stage2_pgd_none(kvm, *pgd))
>   			stage2_flush_puds(kvm, pgd, addr, next);
> +
> +		if (next != end)
> +			cond_resched_lock(&kvm->mmu_lock);
>   	} while (pgd++, addr = next, addr != end);
>   }

Given that this is called under the srcu_lock this looks
good to me:

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>

>   
>   /**
>    * stage2_flush_vm - Invalidate cache for pages mapped in stage 2
>    * @kvm: The struct kvm pointer
>    *
>    * Go through the stage 2 page tables and invalidate any cache lines
>