linux-kernel - Re: [PATCH 02/13] KVM: reuse memslot in kvm_write_guest

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Date:	Tue, 05 May 2015 11:03:26 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	rkrcmar@...hat.com, guangrong.xiao@...ux.intel.com,
	Yang Zhang <yang.z.zhang@...el.com>, wanpeng.li@...ux.intel.com
Subject: Re: [PATCH 02/13] KVM: reuse memslot in kvm_write_guest_page

Paolo Bonzini <pbonzini@...hat.com> writes:

> From: Radim Krčmář <rkrcmar@...hat.com>
>
> Saves one O(log N) search.

It really doesn't hurt to change this to:
"Caching memslot value helps us avoid another O(log N) search
later when calling mark_page_dirty_in_slot()."

Sorry I am not a fan of commit messages less than 75 characters :)
Or you can also call me dumb :)

> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> Message-Id: <1428695247-27603-1-git-send-email-rkrcmar@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  virt/kvm/kvm_main.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 90977418aeb6..b6d415156283 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1590,15 +1590,17 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn, const void *data,
>  			 int offset, int len)
>  {
>  	int r;
> +	struct kvm_memory_slot *memslot;
>  	unsigned long addr;
>  
> -	addr = gfn_to_hva(kvm, gfn);
> +	memslot = gfn_to_memslot(kvm, gfn);
> +	addr = gfn_to_hva_memslot(memslot, gfn);
>  	if (kvm_is_error_hva(addr))
>  		return -EFAULT;
>  	r = __copy_to_user((void __user *)addr + offset, data, len);
>  	if (r)
>  		return -EFAULT;
> -	mark_page_dirty(kvm, gfn);
> +	mark_page_dirty_in_slot(kvm, memslot, gfn);
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(kvm_write_guest_page);
--
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