From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 921AE17A300 for ; Mon, 13 Jul 2026 06:56:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783925796; cv=none; b=MLK2AYUwMbb8y8gnAZ7POXIV9CzJ4XCaLKC8+S0yAtXx2wg2WdiFs5yP0RjS++3CZJ19pprBoYD7jIqNTq+QbVVRGTRM5gjD0zvy4Mz3VZw6lgOU++a4oSgu/QFeVxBGo5NLNrJmRppjwr2HRDFeVHNpBvJbzO0H81MW2otyhgQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783925796; c=relaxed/simple; bh=niiiZtan73ryDXlNQx8+/6p6Ds58BR6uKO8QgjGILIs=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=uqiW51YPpbFWYbFPhHOC1F5TIF4OwzwSuvpPDgJuda9o9OIK+2+7odB/83/QoT7bqKoPS/lNIHkXrMrJgpySTG63bzPugjr973h/8ZxU4wH7z5pRl1VnDFZnVdZHrQHpRMqLCTCkjKVUn2PN6vUPCVoBPgpjWf3JIP+8uQu1lUg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=jHpbrlB9; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="jHpbrlB9" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1783925786; bh=niiiZtan73ryDXlNQx8+/6p6Ds58BR6uKO8QgjGILIs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=jHpbrlB9Lic6LVh5qyMNIdVjwnPAYeBqe3Df03J8igvEp5lL9SN3WmHTBIyvJugxs srX+chsAYyKYEcYpitCoKlh3I0+u6FnfbxjBF5FKuhWPmL9YjDGZYpM6eKMsfIkLQw kduQSf2CK9n2oC+M7J3YkSj4ZaSGsGrRQylEmrLxGMAUg/cdcu93m7pZNhJHa0vgH6 LsPw6bKAp14yFDCf0VpHPTxtBSU3EO4G3AUyJ6TjnihfjOy/01t5p0IL9X70f80qqG r7eErmoMVsgvYCui1hTdYUgA3pp+aTovcIPJcTuwTRVzMHfcnUejteBaqD/DMwEU30 Rgz5PRWn7D1KQ== Received: from fedora-2.home (unknown [100.64.0.11]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange secp256r1 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by bali.collaboradmins.com (Postfix) with ESMTPSA id 3EA6917E010F; Mon, 13 Jul 2026 08:56:26 +0200 (CEST) Date: Mon, 13 Jul 2026 08:56:19 +0200 From: Boris Brezillon To: Ketil Johnsen Cc: Steven Price , Liviu Dudau , 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: <20260713085619.0f2b1197@fedora-2.home> In-Reply-To: <20260712135439.1546950-4-ketil.johnsen@arm.com> References: <20260712135439.1546950-1-ketil.johnsen@arm.com> <20260712135439.1546950-4-ketil.johnsen@arm.com> Organization: Collabora X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sun, 12 Jul 2026 15:54:35 +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 > --- > 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); Could we add the panthor_vm_lock_region() error check in a commit coming before this one, and maybe flag it for backport, with a Fixes tag? > + if (ret) > + return ret; > + > panthor_vm_unmap_pages(vm, unmap_start, unmap_range); > } >