linux-kernel - Re: [PATCH 4/5] vfio/iommu_type1: Carefully use unmap_unpin

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Date:   Tue, 12 Jan 2021 20:04:38 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <kvm@...r.kernel.org>,
        <kvmarm@...ts.cs.columbia.edu>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Will Deacon <will@...nel.org>, "Marc Zyngier" <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Mark Rutland" <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        "Robin Murphy" <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Suzuki K Poulose" <suzuki.poulose@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>,
        <wanghaibin.wang@...wei.com>, <jiangkunkun@...wei.com>
Subject: Re: [PATCH 4/5] vfio/iommu_type1: Carefully use unmap_unpin_all
 during dirty tracking



On 2021/1/12 5:49, Alex Williamson wrote:
> On Thu, 7 Jan 2021 17:29:00 +0800
> Keqian Zhu <zhukeqian1@...wei.com> wrote:
> 
>> If we detach group during dirty page tracking, we shouldn't remove
>> vfio_dma, because dirty log will lose.
>>
>> But we don't prevent unmap_unpin_all in vfio_iommu_release, because
>> under normal procedure, dirty tracking has been stopped.
> 
> This looks like it's creating a larger problem than it's fixing, it's
> not our job to maintain the dirty bitmap regardless of what the user
> does.  If the user detaches the last group in a container causing the
> mappings within that container to be deconstructed before the user has
> collected dirty pages, that sounds like a user error.  A container with
> no groups is de-privileged and therefore loses all state.  Thanks,
> 
> Alex

Hi Alex,

This looks good to me ;-). That's a reasonable constraint for user behavior.

What about replacing this patch with an addition to the uapi document of
VFIO_GROUP_UNSET_CONTAINER? User should pay attention to this when call this
ioctl during dirty tracking.

And any comments on other patches? thanks.

Thanks.
Keqian

> 
>> Fixes: d6a4c185660c ("vfio iommu: Implementation of ioctl for dirty pages tracking")
>> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 14 ++++++++++++--
>>  1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 26b7eb2a5cfc..9776a059904d 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -2373,7 +2373,12 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>>  			if (list_empty(&iommu->external_domain->group_list)) {
>>  				vfio_sanity_check_pfn_list(iommu);
>>  
>> -				if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu))
>> +				/*
>> +				 * During dirty page tracking, we can't remove
>> +				 * vfio_dma because dirty log will lose.
>> +				 */
>> +				if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu) &&
>> +				    !iommu->dirty_page_tracking)
>>  					vfio_iommu_unmap_unpin_all(iommu);
>>  
>>  				kfree(iommu->external_domain);
>> @@ -2406,10 +2411,15 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>>  		 * iommu and external domain doesn't exist, then all the
>>  		 * mappings go away too. If it's the last domain with iommu and
>>  		 * external domain exist, update accounting
>> +		 *
>> +		 * Note: During dirty page tracking, we can't remove vfio_dma
>> +		 * because dirty log will lose. Just update accounting is a good
>> +		 * choice.
>>  		 */
>>  		if (list_empty(&domain->group_list)) {
>>  			if (list_is_singular(&iommu->domain_list)) {
>> -				if (!iommu->external_domain)
>> +				if (!iommu->external_domain &&
>> +				    !iommu->dirty_page_tracking)
>>  					vfio_iommu_unmap_unpin_all(iommu);
>>  				else
>>  					vfio_iommu_unmap_unpin_reaccount(iommu);
> 
> .
>