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Message-ID: <0cf47d65-cb91-199e-af7d-048134634298@huawei.com>
Date: Mon, 18 Jan 2021 21:33:39 +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>, 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 1/6] vfio/iommu_type1: Make an explicit "promote" semantic
On 2021/1/16 6:42, Alex Williamson wrote:
> On Thu, 7 Jan 2021 12:43:56 +0800
> Keqian Zhu <zhukeqian1@...wei.com> wrote:
>
>> When we want to promote the pinned_page_dirty_scope of vfio_iommu,
>> we call the "update" function to visit all vfio_group, but when we
>> want to downgrade this, we can set the flag as false directly.
>
> I agree that the transition can only go in one direction, but it's
> still conditional on the scope of all groups involved. We are
> "updating" the iommu state based on the change of a group. Renaming
> this to "promote" seems like a matter of personal preference.
>
>> So we'd better make an explicit "promote" semantic to the "update"
>> function. BTW, if vfio_iommu already has been promoted, then return
>> early.
>
> Currently it's the caller that avoids using this function when the
> iommu scope is already correct. In fact the changes induces a
> redundant test in the pin_pages code path, we're changing a group from
> non-pinned-page-scope to pinned-page-scope, therefore the iommu scope
> cannot initially be scope limited. In the attach_group call path,
> we're moving that test from the caller, so at best we've introduced an
> additional function call.
>
> The function as it exists today is also more versatile whereas the
> "promote" version here forces it to a single task with no appreciable
> difference in complexity or code. This seems like a frivolous change.
> Thanks,
OK, I will adapt your idea that maintenance a counter of non-pinned groups.
Then we keep the "update" semantic, and the target is the counter ;-).
Thanks,
Keqian
>
> Alex
>
>> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
>> ---
>> drivers/vfio/vfio_iommu_type1.c | 30 ++++++++++++++----------------
>> 1 file changed, 14 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 0b4dedaa9128..334a8240e1da 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -148,7 +148,7 @@ static int put_pfn(unsigned long pfn, int prot);
>> static struct vfio_group *vfio_iommu_find_iommu_group(struct vfio_iommu *iommu,
>> struct iommu_group *iommu_group);
>>
>> -static void update_pinned_page_dirty_scope(struct vfio_iommu *iommu);
>> +static void promote_pinned_page_dirty_scope(struct vfio_iommu *iommu);
>> /*
>> * This code handles mapping and unmapping of user data buffers
>> * into DMA'ble space using the IOMMU
>> @@ -714,7 +714,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>> group = vfio_iommu_find_iommu_group(iommu, iommu_group);
>> if (!group->pinned_page_dirty_scope) {
>> group->pinned_page_dirty_scope = true;
>> - update_pinned_page_dirty_scope(iommu);
>> + promote_pinned_page_dirty_scope(iommu);
>> }
>>
>> goto pin_done;
>> @@ -1622,27 +1622,26 @@ static struct vfio_group *vfio_iommu_find_iommu_group(struct vfio_iommu *iommu,
>> return group;
>> }
>>
>> -static void update_pinned_page_dirty_scope(struct vfio_iommu *iommu)
>> +static void promote_pinned_page_dirty_scope(struct vfio_iommu *iommu)
>> {
>> struct vfio_domain *domain;
>> struct vfio_group *group;
>>
>> + if (iommu->pinned_page_dirty_scope)
>> + return;
>> +
>> list_for_each_entry(domain, &iommu->domain_list, next) {
>> list_for_each_entry(group, &domain->group_list, next) {
>> - if (!group->pinned_page_dirty_scope) {
>> - iommu->pinned_page_dirty_scope = false;
>> + if (!group->pinned_page_dirty_scope)
>> return;
>> - }
>> }
>> }
>>
>> if (iommu->external_domain) {
>> domain = iommu->external_domain;
>> list_for_each_entry(group, &domain->group_list, next) {
>> - if (!group->pinned_page_dirty_scope) {
>> - iommu->pinned_page_dirty_scope = false;
>> + if (!group->pinned_page_dirty_scope)
>> return;
>> - }
>> }
>> }
>>
>> @@ -2057,8 +2056,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>> * addition of a dirty tracking group.
>> */
>> group->pinned_page_dirty_scope = true;
>> - if (!iommu->pinned_page_dirty_scope)
>> - update_pinned_page_dirty_scope(iommu);
>> + promote_pinned_page_dirty_scope(iommu);
>> mutex_unlock(&iommu->lock);
>>
>> return 0;
>> @@ -2341,7 +2339,7 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>> struct vfio_iommu *iommu = iommu_data;
>> struct vfio_domain *domain;
>> struct vfio_group *group;
>> - bool update_dirty_scope = false;
>> + bool promote_dirty_scope = false;
>> LIST_HEAD(iova_copy);
>>
>> mutex_lock(&iommu->lock);
>> @@ -2349,7 +2347,7 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>> if (iommu->external_domain) {
>> group = find_iommu_group(iommu->external_domain, iommu_group);
>> if (group) {
>> - update_dirty_scope = !group->pinned_page_dirty_scope;
>> + promote_dirty_scope = !group->pinned_page_dirty_scope;
>> list_del(&group->next);
>> kfree(group);
>>
>> @@ -2379,7 +2377,7 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>> continue;
>>
>> vfio_iommu_detach_group(domain, group);
>> - update_dirty_scope = !group->pinned_page_dirty_scope;
>> + promote_dirty_scope = !group->pinned_page_dirty_scope;
>> list_del(&group->next);
>> kfree(group);
>> /*
>> @@ -2415,8 +2413,8 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>> * Removal of a group without dirty tracking may allow the iommu scope
>> * to be promoted.
>> */
>> - if (update_dirty_scope)
>> - update_pinned_page_dirty_scope(iommu);
>> + if (promote_dirty_scope)
>> + promote_pinned_page_dirty_scope(iommu);
>> mutex_unlock(&iommu->lock);
>> }
>>
>
> .
>
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