From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9F341C54FDF for ; Thu, 30 Jul 2026 10:47:49 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id D916510EE94; Thu, 30 Jul 2026 10:47:48 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=arm.com header.i=@arm.com header.b="RyAIqM+S"; dkim-atps=neutral Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by gabe.freedesktop.org (Postfix) with ESMTP id CBC7C10EE94 for ; Thu, 30 Jul 2026 10:47:47 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3C64F1688 for ; Thu, 30 Jul 2026 03:47:43 -0700 (PDT) Received: from [10.2.11.34] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 10F5B3F86F for ; Thu, 30 Jul 2026 03:47:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785408467; bh=unSsqLjMlbRj1rOildUEgSOScIlD71euFOCQoiPmzqA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RyAIqM+SfrvuQMy/k7nbz5Q+wWWuIgrNQZ9+Nnaf3lQwAdNmUuEuHyNOAzrIvBaqM F77xfIMdgHTJWipsZgNM1furDg1C9pDENzeSwkfso1vUQ2cR3ucRqN3mWwS2f3c2E7 4Vm8nn1F8GtPS30JxUH/9Xvfj0XrOFUb3RJDhQyw= Date: Thu, 30 Jul 2026 11:47:34 +0100 From: Liviu Dudau To: Ketil Johnsen Cc: Boris Brezillon , Steven Price , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Daniel Almeida , Alice Ryhl , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/7] drm/panthor: Explicit expansion of locked VM region Message-ID: References: <20260712135439.1546950-1-ketil.johnsen@arm.com> <20260712135439.1546950-4-ketil.johnsen@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260712135439.1546950-4-ketil.johnsen@arm.com> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Sun, Jul 12, 2026 at 03:54:35PM +0200, Ketil Johnsen wrote: > Currently the panthor_vm_lock_region() function will implicitly expand > an already locked VM region. This can be problematic because the caller > do not reliably know if it needs to call panthor_vm_unlock_region() > or not. > > Worth noting, there is currently no known issues with this as the code > is written today. > > This change introduces panthor_vm_expand_region() which will only work > if there is already a locked VM region. This again means that the > original lock and unlock functions can work as a pair. This pairing is > needed for subsequent protected memory changes. > > Signed-off-by: Ketil Johnsen Reviewed-by: Liviu Dudau Best regards, Liviu > --- > drivers/gpu/drm/panthor/panthor_mmu.c | 87 +++++++++++++++++++-------- > 1 file changed, 62 insertions(+), 25 deletions(-) > > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c > index 1f6b9242279c2..b82b01013611c 100644 > --- a/drivers/gpu/drm/panthor/panthor_mmu.c > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c > @@ -1774,20 +1774,49 @@ static const char *access_type_name(struct panthor_device *ptdev, > } > } > > +static int panthor_vm_apply_as_lock(struct panthor_vm *vm, u64 region) > +{ > + struct panthor_device *ptdev = vm->ptdev; > + > + lockdep_assert_held(&ptdev->mmu->as.slots_lock); > + > + gpu_write64(ptdev->mmu->iomem, AS_LOCKADDR(vm->as.id), region); > + return as_send_cmd_and_wait(ptdev, vm->as.id, AS_COMMAND_LOCK); > +} > + > static int panthor_vm_lock_region(struct panthor_vm *vm, u64 start, u64 size) > { > struct panthor_device *ptdev = vm->ptdev; > int ret = 0; > > - /* sm_step_remap() can call panthor_vm_lock_region() to account for > - * the wider unmap needed when doing a partial huge page unamp. We > - * need to ignore the lock if it's already part of the locked region. > - */ > - if (start >= vm->locked_region.start && > - start + size <= vm->locked_region.start + vm->locked_region.size) > - return 0; > + if (drm_WARN_ON(&ptdev->base, vm->locked_region.size)) > + return -EINVAL; > + > + mutex_lock(&ptdev->mmu->as.slots_lock); > + if (vm->as.id >= 0 && size) { > + u64 region = pack_region_range(ptdev, &start, &size); > + > + ret = panthor_vm_apply_as_lock(vm, region); > + } > > - /* sm_step_remap() may need a locked region that isn't a strict superset > + if (!ret) { > + vm->locked_region.start = start; > + vm->locked_region.size = size; > + } > + mutex_unlock(&ptdev->mmu->as.slots_lock); > + > + return ret; > +} > + > +static int panthor_vm_expand_locked_region(struct panthor_vm *vm, > + u64 start, u64 size) > +{ > + struct panthor_device *ptdev = vm->ptdev; > + u64 end; > + int ret = 0; > + > + /* This function is here to handle the following case: > + * sm_step_remap() may need a locked region that isn't a strict superset > * of the original one because of having to extend unmap boundaries beyond > * it to deal with partial unmaps of transparent huge pages. What we want > * in those cases is to lock the union of both regions. The new region must > @@ -1795,25 +1824,30 @@ static int panthor_vm_lock_region(struct panthor_vm *vm, u64 start, u64 size) > * boundaries in a remap operation can only shift up or down respectively, > * but never otherwise. > */ > - if (vm->locked_region.size) { > - u64 end = max(vm->locked_region.start + vm->locked_region.size, > - start + size); > > - drm_WARN_ON_ONCE(&vm->ptdev->base, (start + size <= vm->locked_region.start) || > - (start >= vm->locked_region.start + vm->locked_region.size)); > + /* This function can only expand an already locked region */ > + if (drm_WARN_ON(&ptdev->base, !vm->locked_region.size)) > + return -EINVAL; > + > + /* Early out if requested range is already locked */ > + if (start >= vm->locked_region.start && > + start + size <= vm->locked_region.start + vm->locked_region.size) > + return 0; > > - start = min(start, vm->locked_region.start); > - size = end - start; > - } > + end = max(vm->locked_region.start + vm->locked_region.size, > + start + size); > + > + drm_WARN_ON_ONCE(&ptdev->base, (start + size <= vm->locked_region.start) || > + (start >= vm->locked_region.start + vm->locked_region.size)); > + > + start = min(start, vm->locked_region.start); > + size = end - start; > > mutex_lock(&ptdev->mmu->as.slots_lock); > if (vm->as.id >= 0 && size) { > - /* Lock the region that needs to be updated */ > - gpu_write64(ptdev->mmu->iomem, AS_LOCKADDR(vm->as.id), > - pack_region_range(ptdev, &start, &size)); > + u64 region = pack_region_range(ptdev, &start, &size); > > - /* If the lock succeeded, update the locked_region info. */ > - ret = as_send_cmd_and_wait(ptdev, vm->as.id, AS_COMMAND_LOCK); > + ret = panthor_vm_apply_as_lock(vm, region); > } > > if (!ret) { > @@ -2367,11 +2401,14 @@ static int panthor_gpuva_sm_step_remap(struct drm_gpuva_op *op, > */ > unmap_hugepage_align(&op->remap, &unmap_start, &unmap_range); > > - /* If the range changed, we might have to lock a wider region to guarantee > - * atomicity. panthor_vm_lock_region() bails out early if the new region > - * is already part of the locked region, so no need to do this check here. > + /* If the range changed, we might have to lock a wider region to > + * guarantee atomicity. > */ > - panthor_vm_lock_region(vm, unmap_start, unmap_range); > + ret = panthor_vm_expand_locked_region(vm, unmap_start, > + unmap_range); > + if (ret) > + return ret; > + > panthor_vm_unmap_pages(vm, unmap_start, unmap_range); > } > > -- > 2.43.0 > -- ==================== | I would like to | | fix the world, | | but they're not | | giving me the | \ source code! / --------------- ¯\_(ツ)_/¯