linux-kernel - Re: [PATCH v4 2/2] kvm/arm64: Try stage2 block mapping for host device MMIO

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Message-ID: <d8af7360-ee96-2344-336d-bfaf8828fc8e@huawei.com>
Date:   Sat, 17 Apr 2021 09:05:05 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <kvm@...r.kernel.org>,
        <kvmarm@...ts.cs.columbia.edu>, <wanghaibin.wang@...wei.com>
Subject: Re: [PATCH v4 2/2] kvm/arm64: Try stage2 block mapping for host
 device MMIO

Hi Marc,

On 2021/4/16 22:44, Marc Zyngier wrote:
> On Thu, 15 Apr 2021 15:08:09 +0100,
> Keqian Zhu <zhukeqian1@...wei.com> wrote:
>>
>> Hi Marc,
>>
>> On 2021/4/15 22:03, Keqian Zhu wrote:
>>> The MMIO region of a device maybe huge (GB level), try to use
>>> block mapping in stage2 to speedup both map and unmap.
>>>
>>> Compared to normal memory mapping, we should consider two more
>>> points when try block mapping for MMIO region:
>>>
>>> 1. For normal memory mapping, the PA(host physical address) and
>>> HVA have same alignment within PUD_SIZE or PMD_SIZE when we use
>>> the HVA to request hugepage, so we don't need to consider PA
>>> alignment when verifing block mapping. But for device memory
>>> mapping, the PA and HVA may have different alignment.
>>>
>>> 2. For normal memory mapping, we are sure hugepage size properly
>>> fit into vma, so we don't check whether the mapping size exceeds
>>> the boundary of vma. But for device memory mapping, we should pay
>>> attention to this.
>>>
>>> This adds get_vma_page_shift() to get page shift for both normal
>>> memory and device MMIO region, and check these two points when
>>> selecting block mapping size for MMIO region.
>>>
>>> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
>>> ---
>>>  arch/arm64/kvm/mmu.c | 61 ++++++++++++++++++++++++++++++++++++--------
>>>  1 file changed, 51 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>>> index c59af5ca01b0..5a1cc7751e6d 100644
>>> --- a/arch/arm64/kvm/mmu.c
>>> +++ b/arch/arm64/kvm/mmu.c
>>> @@ -738,6 +738,35 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
>>>  	return PAGE_SIZE;
>>>  }
>>>  
[...]

>>> +	/*
>>> +	 * logging_active is guaranteed to never be true for VM_PFNMAP
>>> +	 * memslots.
>>> +	 */
>>> +	if (logging_active) {
>>>  		force_pte = true;
>>>  		vma_shift = PAGE_SHIFT;
>>> +	} else {
>>> +		vma_shift = get_vma_page_shift(vma, hva);
>>>  	}
>> I use a if/else manner in v4, please check that. Thanks very much!
> 
> That's fine. However, it is getting a bit late for 5.13, and we don't
> have much time to left it simmer in -next. I'll probably wait until
> after the merge window to pick it up.
OK, no problem. Thanks! :)

BRs,
Keqian