Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754247AbdDQVcb (ORCPT ); Mon, 17 Apr 2017 17:32:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45610 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751852AbdDQVc2 (ORCPT ); Mon, 17 Apr 2017 17:32:28 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 47F908814 Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=alex.williamson@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 47F908814 Date: Mon, 17 Apr 2017 15:32:20 -0600 From: Alex Williamson To: Kirti Wankhede Cc: Peter Xu , , , , Subject: Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue Message-ID: <20170417153220.531a0600@t450s.home> In-Reply-To: References: <20170417014142.25866.16852.stgit@gimli.home> <20170417014227.25866.59899.stgit@gimli.home> <20170417064754.GC16703@pxdev.xzpeter.org> <20170417083201.043cedbf@t450s.home> <71c0bcf5-9d73-c875-aa3f-482472027e7a@nvidia.com> <20170417131926.54af5181@t450s.home> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Mon, 17 Apr 2017 21:32:27 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10899 Lines: 316 On Tue, 18 Apr 2017 01:02:12 +0530 Kirti Wankhede wrote: > On 4/18/2017 12:49 AM, Alex Williamson wrote: > > On Tue, 18 Apr 2017 00:35:06 +0530 > > Kirti Wankhede wrote: > > > >> On 4/17/2017 8:02 PM, Alex Williamson wrote: > >>> On Mon, 17 Apr 2017 14:47:54 +0800 > >>> Peter Xu wrote: > >>> > >>>> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote: > >>>> > >>>> [...] > >>>> > >>>>> -static void vfio_lock_acct(struct task_struct *task, long npage) > >>>>> +static int vfio_lock_acct(struct task_struct *task, long npage, bool lock_cap) > >>>>> { > >>>>> - struct vwork *vwork; > >>>>> struct mm_struct *mm; > >>>>> bool is_current; > >>>>> + int ret; > >>>>> > >>>>> if (!npage) > >>>>> - return; > >>>>> + return 0; > >>>>> > >>>>> is_current = (task->mm == current->mm); > >>>>> > >>>>> mm = is_current ? task->mm : get_task_mm(task); > >>>>> if (!mm) > >>>>> - return; /* process exited */ > >>>>> + return -ESRCH; /* process exited */ > >>>>> > >>>>> - if (down_write_trylock(&mm->mmap_sem)) { > >>>>> - mm->locked_vm += npage; > >>>>> - up_write(&mm->mmap_sem); > >>>>> - if (!is_current) > >>>>> - mmput(mm); > >>>>> - return; > >>>>> - } > >>>>> + ret = down_write_killable(&mm->mmap_sem); > >>>>> + if (!ret) { > >>>>> + if (npage < 0 || lock_cap) { > >>>> > >>>> Nit: maybe we can avoid passing in lock_cap in all the callers of > >>>> vfio_lock_acct() and fetch it via has_capability() only if npage < 0? > >>>> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't > >>>> need to pass in "false" any time when doing unpins. > >>> > >>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap > >>> since it tests whether the user is exceeding their locked memory > >>> limit. The other callers could certainly get away with > >>> vfio_lock_acct() testing the capability itself but that would add a > >>> redundant call for the most common user. I'm not a big fan of passing > >>> a lock_cap bool either, but it seemed the best fix for now. The > >>> cleanest alternative I can up with is this (untested): > >>> > >> > >> In my opinion, passing 'bool lock_cap' looks much clean and simple. > >> > >> Reviewed-by: Kirti Wankhede > > > > Well shoot, I was just starting to warm up to the bool*. I like that > > we're not presuming the polarity for the callers we expect to be > > removing pages and I generally just dislike passing fixed bool > > parameters to change the function behavior. I've cleaned it up a bit > > further and was starting to do some testing on this which I'd propose > > for v5. Does it change your opinion? > > If passing fixed bool parameter is the concern then I would lean towards > Peter's suggestion. vfio_pin_pages_remote() will check lock capability > outside vfio_lock_acct() and again in vfio_lock_acct(). At other places, > it will be takes care within vfio_lock_acct() Sorry, I don't see that as a viable option. Testing for CAP_IPC_LOCK in both vfio_pin_pages_remote() and vfio_lock_acct() results in over a 10% performance hit on the mapping path with a custom micro-benchmark. In fact, it suggests we should probably pass that from even higher in the call stack. Thanks, Alex > > > > commit cd61c5f507d614ac14b75b0a548c8738deff88ea > > Author: Alex Williamson > > Date: Thu Apr 13 14:10:15 2017 -0600 > > > > vfio/type1: Remove locked page accounting workqueue > > > > If the mmap_sem is contented then the vfio type1 IOMMU backend will > > defer locked page accounting updates to a workqueue task. This has a > > few problems and depending on which side the user tries to play, they > > might be over-penalized for unmaps that haven't yet been accounted or > > race the workqueue to enter more mappings than they're allowed. The > > original intent of this workqueue mechanism seems to be focused on > > reducing latency through the ioctl, but we cannot do so at the cost > > of correctness. Remove this workqueue mechanism and update the > > callers to allow for failure. We can also now recheck the limit under > > write lock to make sure we don't exceed it. > > > > vfio_pin_pages_remote() also now necessarily includes an unwind path > > which we can jump to directly if the consecutive page pinning finds > > that we're exceeding the user's memory limits. This avoids the > > current lazy approach which does accounting and mapping up to the > > fault, only to return an error on the next iteration to unwind the > > entire vfio_dma. > > > > Cc: stable@vger.kernel.org > > Signed-off-by: Alex Williamson > > > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > > index 32d2633092a3..a8a079ba9477 100644 > > --- a/drivers/vfio/vfio_iommu_type1.c > > +++ b/drivers/vfio/vfio_iommu_type1.c > > @@ -246,69 +246,46 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn) > > return ret; > > } > > > > -struct vwork { > > - struct mm_struct *mm; > > - long npage; > > - struct work_struct work; > > -}; > > - > > -/* delayed decrement/increment for locked_vm */ > > -static void vfio_lock_acct_bg(struct work_struct *work) > > -{ > > - struct vwork *vwork = container_of(work, struct vwork, work); > > - struct mm_struct *mm; > > - > > - mm = vwork->mm; > > - down_write(&mm->mmap_sem); > > - mm->locked_vm += vwork->npage; > > - up_write(&mm->mmap_sem); > > - mmput(mm); > > - kfree(vwork); > > -} > > - > > -static void vfio_lock_acct(struct task_struct *task, long npage) > > +static int vfio_lock_acct(struct task_struct *task, long npage, bool *lock_cap) > > { > > - struct vwork *vwork; > > struct mm_struct *mm; > > bool is_current; > > + int ret; > > > > if (!npage) > > - return; > > + return 0; > > > > is_current = (task->mm == current->mm); > > > > mm = is_current ? task->mm : get_task_mm(task); > > if (!mm) > > - return; /* process exited */ > > + return -ESRCH; /* process exited */ > > > > - if (down_write_trylock(&mm->mmap_sem)) { > > - mm->locked_vm += npage; > > - up_write(&mm->mmap_sem); > > - if (!is_current) > > - mmput(mm); > > - return; > > - } > > + ret = down_write_killable(&mm->mmap_sem); > > + if (!ret) { > > + if (npage > 0) { > > + if (lock_cap ? !*lock_cap : > > + !has_capability(task, CAP_IPC_LOCK)) { > > + unsigned long limit; > > + > > + limit = task_rlimit(task, > > + RLIMIT_MEMLOCK) >> PAGE_SHIFT; > > + > > + if (mm->locked_vm + npage > limit) > > + ret = -ENOMEM; > > + } > > + } > > + > > + if (!ret) > > + mm->locked_vm += npage; > > > > - if (is_current) { > > - mm = get_task_mm(task); > > - if (!mm) > > - return; > > + up_write(&mm->mmap_sem); > > } > > > > - /* > > - * Couldn't get mmap_sem lock, so must setup to update > > - * mm->locked_vm later. If locked_vm were atomic, we > > - * wouldn't need this silliness > > - */ > > - vwork = kmalloc(sizeof(struct vwork), GFP_KERNEL); > > - if (WARN_ON(!vwork)) { > > + if (!is_current) > > mmput(mm); > > - return; > > - } > > - INIT_WORK(&vwork->work, vfio_lock_acct_bg); > > - vwork->mm = mm; > > - vwork->npage = npage; > > - schedule_work(&vwork->work); > > + > > + return ret; > > } > > > > /* > > @@ -405,7 +382,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > > static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr, > > long npage, unsigned long *pfn_base) > > { > > - unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT; > > + unsigned long pfn = 0, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT; > > bool lock_cap = capable(CAP_IPC_LOCK); > > long ret, pinned = 0, lock_acct = 0; > > bool rsvd; > > @@ -442,8 +419,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr, > > /* Lock all the consecutive pages from pfn_base */ > > for (vaddr += PAGE_SIZE, iova += PAGE_SIZE; pinned < npage; > > pinned++, vaddr += PAGE_SIZE, iova += PAGE_SIZE) { > > - unsigned long pfn = 0; > > - > > ret = vaddr_get_pfn(current->mm, vaddr, dma->prot, &pfn); > > if (ret) > > break; > > @@ -460,14 +435,25 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr, > > put_pfn(pfn, dma->prot); > > pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n", > > __func__, limit << PAGE_SHIFT); > > - break; > > + ret = -ENOMEM; > > + goto unpin_out; > > } > > lock_acct++; > > } > > } > > > > out: > > - vfio_lock_acct(current, lock_acct); > > + ret = vfio_lock_acct(current, lock_acct, &lock_cap); > > + > > +unpin_out: > > + if (ret) { > > + if (!rsvd) { > > + for (pfn = *pfn_base ; pinned ; pfn++, pinned--) > > + put_pfn(pfn, dma->prot); > > + } > > + > > + return ret; > > + } > > > > return pinned; > > } > > @@ -488,7 +474,7 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, dma_addr_t iova, > > } > > > > if (do_accounting) > > - vfio_lock_acct(dma->task, locked - unlocked); > > + vfio_lock_acct(dma->task, locked - unlocked, NULL); > > > > return unlocked; > > } > > @@ -522,8 +508,14 @@ static int vfio_pin_page_external(struct vfio_dma *dma, unsigned long vaddr, > > goto pin_page_exit; > > } > > > > - if (!rsvd && do_accounting) > > - vfio_lock_acct(dma->task, 1); > > + if (!rsvd && do_accounting) { > > + ret = vfio_lock_acct(dma->task, 1, &lock_cap); > > + if (ret) { > > + put_pfn(*pfn_base, dma->prot); > > + goto pin_page_exit; > > + } > > + } > > + > > ret = 1; > > > > pin_page_exit: > > @@ -543,7 +535,7 @@ static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova, > > unlocked = vfio_iova_put_vfio_pfn(dma, vpfn); > > > > if (do_accounting) > > - vfio_lock_acct(dma->task, -unlocked); > > + vfio_lock_acct(dma->task, -unlocked, NULL); > > > > return unlocked; > > } > > @@ -740,7 +732,7 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma, > > > > dma->iommu_mapped = false; > > if (do_accounting) { > > - vfio_lock_acct(dma->task, -unlocked); > > + vfio_lock_acct(dma->task, -unlocked, NULL); > > return 0; > > } > > return unlocked; > > @@ -1382,7 +1374,7 @@ static void vfio_iommu_unmap_unpin_reaccount(struct vfio_iommu *iommu) > > if (!is_invalid_reserved_pfn(vpfn->pfn)) > > locked++; > > } > > - vfio_lock_acct(dma->task, locked - unlocked); > > + vfio_lock_acct(dma->task, locked - unlocked, NULL); > > } > > } > > > > > > Patch 2/2 would clearly change the &lock_cap in > > vfio_pin_page_external() to a NULL, so only _remote passes a pointer > > there. Thanks, > > > > Alex > >