Re: [PATCH 1/2] vfio powerpc: implemented IOMMU driver for VFIO

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 2012-11-27 at 15:58 +1100, Alexey Kardashevskiy wrote:
> On 27/11/12 15:29, Alex Williamson wrote:
> > On Tue, 2012-11-27 at 15:06 +1100, Alexey Kardashevskiy wrote:
> >> On 27/11/12 05:20, Alex Williamson wrote:
> >>> On Fri, 2012-11-23 at 20:03 +1100, Alexey Kardashevskiy wrote:
> >>>> VFIO implements platform independent stuff such as
> >>>> a PCI driver, BAR access (via read/write on a file descriptor
> >>>> or direct mapping when possible) and IRQ signaling.
> >>>>
> >>>> The platform dependent part includes IOMMU initialization
> >>>> and handling. This patch implements an IOMMU driver for VFIO
> >>>> which does mapping/unmapping pages for the guest IO and
> >>>> provides information about DMA window (required by a POWERPC
> >>>> guest).
> >>>>
> >>>> The counterpart in QEMU is required to support this functionality.
> >>>>
> >>>> Cc: David Gibson <david@gibson.dropbear.id.au>
> >>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>>> ---
> >>>>    drivers/vfio/Kconfig                |    6 +
> >>>>    drivers/vfio/Makefile               |    1 +
> >>>>    drivers/vfio/vfio_iommu_spapr_tce.c |  247 +++++++++++++++++++++++++++++++++++
> >>>>    include/linux/vfio.h                |   20 +++
> >>>>    4 files changed, 274 insertions(+)
> >>>>    create mode 100644 drivers/vfio/vfio_iommu_spapr_tce.c
> >>>>
> >>>> diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
> >>>> index 7cd5dec..b464687 100644
> >>>> --- a/drivers/vfio/Kconfig
> >>>> +++ b/drivers/vfio/Kconfig
> >>>> @@ -3,10 +3,16 @@ config VFIO_IOMMU_TYPE1
> >>>>    	depends on VFIO
> >>>>    	default n
> >>>>
> >>>> +config VFIO_IOMMU_SPAPR_TCE
> >>>> +	tristate
> >>>> +	depends on VFIO && SPAPR_TCE_IOMMU
> >>>> +	default n
> >>>> +
> >>>>    menuconfig VFIO
> >>>>    	tristate "VFIO Non-Privileged userspace driver framework"
> >>>>    	depends on IOMMU_API
> >>>>    	select VFIO_IOMMU_TYPE1 if X86
> >>>> +	select VFIO_IOMMU_SPAPR_TCE if PPC_POWERNV
> >>>>    	help
> >>>>    	  VFIO provides a framework for secure userspace device drivers.
> >>>>    	  See Documentation/vfio.txt for more details.
> >>>> diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
> >>>> index 2398d4a..72bfabc 100644
> >>>> --- a/drivers/vfio/Makefile
> >>>> +++ b/drivers/vfio/Makefile
> >>>> @@ -1,3 +1,4 @@
> >>>>    obj-$(CONFIG_VFIO) += vfio.o
> >>>>    obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
> >>>> +obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
> >>>>    obj-$(CONFIG_VFIO_PCI) += pci/
> >>>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> >>>> new file mode 100644
> >>>> index 0000000..46a6298
> >>>> --- /dev/null
> >>>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> >>>> @@ -0,0 +1,247 @@
> >>>> +/*
> >>>> + * VFIO: IOMMU DMA mapping support for TCE on POWER
> >>>> + *
> >>>> + * Copyright (C) 2012 IBM Corp.  All rights reserved.
> >>>> + *     Author: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>>> + *
> >>>> + * This program is free software; you can redistribute it and/or modify
> >>>> + * it under the terms of the GNU General Public License version 2 as
> >>>> + * published by the Free Software Foundation.
> >>>> + *
> >>>> + * Derived from original vfio_iommu_type1.c:
> >>>> + * Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
> >>>> + *     Author: Alex Williamson <alex.williamson@redhat.com>
> >>>> + */
> >>>> +
> >>>> +#include <linux/module.h>
> >>>> +#include <linux/pci.h>
> >>>> +#include <linux/slab.h>
> >>>> +#include <linux/uaccess.h>
> >>>> +#include <linux/err.h>
> >>>> +#include <linux/vfio.h>
> >>>> +#include <asm/iommu.h>
> >>>> +
> >>>> +#define DRIVER_VERSION  "0.1"
> >>>> +#define DRIVER_AUTHOR   "aik@ozlabs.ru"
> >>>> +#define DRIVER_DESC     "VFIO IOMMU SPAPR TCE"
> >>>> +
> >>>> +static void tce_iommu_detach_group(void *iommu_data,
> >>>> +		struct iommu_group *iommu_group);
> >>>> +
> >>>> +/*
> >>>> + * VFIO IOMMU fd for SPAPR_TCE IOMMU implementation
> >>>> + */
> >>>> +
> >>>> +/*
> >>>> + * The container descriptor supports only a single group per container.
> >>>> + * Required by the API as the container is not supplied with the IOMMU group
> >>>> + * at the moment of initialization.
> >>>> + */
> >>>> +struct tce_container {
> >>>> +	struct mutex lock;
> >>>> +	struct iommu_table *tbl;
> >>>> +};
> >>>> +
> >>>> +static void *tce_iommu_open(unsigned long arg)
> >>>> +{
> >>>> +	struct tce_container *container;
> >>>> +
> >>>> +	if (arg != VFIO_SPAPR_TCE_IOMMU) {
> >>>> +		printk(KERN_ERR "tce_vfio: Wrong IOMMU type\n");
> >>>> +		return ERR_PTR(-EINVAL);
> >>>> +	}
> >>>> +
> >>>> +	container = kzalloc(sizeof(*container), GFP_KERNEL);
> >>>> +	if (!container)
> >>>> +		return ERR_PTR(-ENOMEM);
> >>>> +
> >>>> +	mutex_init(&container->lock);
> >>>> +
> >>>> +	return container;
> >>>> +}
> >>>> +
> >>>> +static void tce_iommu_release(void *iommu_data)
> >>>> +{
> >>>> +	struct tce_container *container = iommu_data;
> >>>> +
> >>>> +	WARN_ON(container->tbl && !container->tbl->it_group);
> >>>
> >>> I think your patch ordering is backwards here.  it_group isn't added
> >>> until 2/2.  I'd really like to see the arch/powerpc code approved and
> >>> merged by the powerpc maintainer before we add the code that makes use
> >>> of it into vfio.  Otherwise we just get lots of churn if interfaces
> >>> change or they disapprove of it altogether.
> >>
> >>
> >> Makes sense, thanks.
> >>
> >>
> >>>> +	if (container->tbl && container->tbl->it_group)
> >>>> +		tce_iommu_detach_group(iommu_data, container->tbl->it_group);
> >>>> +
> >>>> +	mutex_destroy(&container->lock);
> >>>> +
> >>>> +	kfree(container);
> >>>> +}
> >>>> +
> >>>> +static long tce_iommu_ioctl(void *iommu_data,
> >>>> +				 unsigned int cmd, unsigned long arg)
> >>>> +{
> >>>> +	struct tce_container *container = iommu_data;
> >>>> +	unsigned long minsz;
> >>>> +
> >>>> +	switch (cmd) {
> >>>> +	case VFIO_CHECK_EXTENSION: {
> >>>> +		return (arg == VFIO_SPAPR_TCE_IOMMU) ? 1 : 0;
> >>>> +	}
> >>>> +	case VFIO_IOMMU_SPAPR_TCE_GET_INFO: {
> >>>> +		struct vfio_iommu_spapr_tce_info info;
> >>>> +		struct iommu_table *tbl = container->tbl;
> >>>> +
> >>>> +		if (WARN_ON(!tbl))
> >>>> +			return -ENXIO;
> >>>> +
> >>>> +		minsz = offsetofend(struct vfio_iommu_spapr_tce_info,
> >>>> +				dma64_window_size);
> >>>> +
> >>>> +		if (copy_from_user(&info, (void __user *)arg, minsz))
> >>>> +			return -EFAULT;
> >>>> +
> >>>> +		if (info.argsz < minsz)
> >>>> +			return -EINVAL;
> >>>> +
> >>>> +		info.dma32_window_start = tbl->it_offset << IOMMU_PAGE_SHIFT;
> >>>> +		info.dma32_window_size = tbl->it_size << IOMMU_PAGE_SHIFT;
> >>>> +		info.dma64_window_start = 0;
> >>>> +		info.dma64_window_size = 0;
> >>>> +		info.flags = 0;
> >>>> +
> >>>> +		if (copy_to_user((void __user *)arg, &info, minsz))
> >>>> +			return -EFAULT;
> >>>> +
> >>>> +		return 0;
> >>>> +	}
> >>>> +	case VFIO_IOMMU_MAP_DMA: {
> >>>> +		vfio_iommu_spapr_tce_dma_map param;
> >>>> +		struct iommu_table *tbl = container->tbl;
> >>>> +		enum dma_data_direction direction = DMA_NONE;
> >>>> +
> >>>> +		if (WARN_ON(!tbl))
> >>>> +			return -ENXIO;
> >>>> +
> >>>> +		minsz = offsetofend(vfio_iommu_spapr_tce_dma_map, size);
> >>>> +
> >>>> +		if (copy_from_user(&param, (void __user *)arg, minsz))
> >>>> +			return -EFAULT;
> >>>> +
> >>>> +		if (param.argsz < minsz)
> >>>> +			return -EINVAL;
> >>>> +
> >>>> +		if ((param.flags & VFIO_DMA_MAP_FLAG_READ) &&
> >>>> +				(param.flags & VFIO_DMA_MAP_FLAG_WRITE)) {
> >>>> +			direction = DMA_BIDIRECTIONAL;
> >>>> +		} else if (param.flags & VFIO_DMA_MAP_FLAG_READ) {
> >>>> +			direction = DMA_TO_DEVICE;
> >>>> +		} else if (param.flags & VFIO_DMA_MAP_FLAG_WRITE) {
> >>>> +			direction = DMA_FROM_DEVICE;
> >>>> +		}
> >>>> +
> >>>> +		param.size += param.iova & ~IOMMU_PAGE_MASK;
> >>>> +		param.size = _ALIGN_UP(param.size, IOMMU_PAGE_SIZE);
> >>>
> >>> On x86 we force iova, vaddr, and size to all be aligned to the smallest
> >>> page granularity of the iommu and return -EINVAL if it doesn't fit.
> >>> What does it imply to the user if they're always aligned to work here?
> >>> Won't this interface happily map overlapping entries with no indication
> >>> to the user that the previous mapping is no longer valid?
> >>> Maybe another reason why a combined unmap/map makes me nervous, we have
> >>> to assume the user knows what they're doing.
> >>
> >>
> >> I got used to guests which do know what they are doing so I am pretty calm :)
> >> but ok, I'll move alignment to the QEMU, it makes sense.
> >>
> >>
> >>>> +
> >>>> +		return iommu_put_tces(tbl, param.iova >> IOMMU_PAGE_SHIFT,
> >>>> +				param.vaddr & IOMMU_PAGE_MASK, direction,
> >>>> +				param.size >> IOMMU_PAGE_SHIFT);
> >>>> +	}
> >>>> +	case VFIO_IOMMU_UNMAP_DMA: {
> >>>> +		vfio_iommu_spapr_tce_dma_unmap param;
> >>>> +		struct iommu_table *tbl = container->tbl;
> >>>> +
> >>>> +		if (WARN_ON(!tbl))
> >>>> +			return -ENXIO;
> >>>> +
> >>>> +		minsz = offsetofend(vfio_iommu_spapr_tce_dma_unmap, size);
> >>>> +
> >>>> +		if (copy_from_user(&param, (void __user *)arg, minsz))
> >>>> +			return -EFAULT;
> >>>> +
> >>>> +		if (param.argsz < minsz)
> >>>> +			return -EINVAL;
> >>>> +
> >>>> +		param.size += param.iova & ~IOMMU_PAGE_MASK;
> >>>> +		param.size = _ALIGN_UP(param.size, IOMMU_PAGE_SIZE);
> >>>> +
> >>>> +		return iommu_put_tces(tbl, param.iova >> IOMMU_PAGE_SHIFT,
> >>>> +				0, DMA_NONE, param.size >> IOMMU_PAGE_SHIFT);
> >>>> +	}
> >>>> +	default:
> >>>> +		printk(KERN_WARNING "tce_vfio: unexpected cmd %x\n", cmd);
> >>>
> >>> pr_warn
> >>>
> >>>> +	}
> >>>> +
> >>>> +	return -ENOTTY;
> >>>> +}
> >>>> +
> >>>> +static int tce_iommu_attach_group(void *iommu_data,
> >>>> +		struct iommu_group *iommu_group)
> >>>> +{
> >>>> +	struct tce_container *container = iommu_data;
> >>>> +	struct iommu_table *tbl = iommu_group_get_iommudata(iommu_group);
> >>>> +
> >>>> +	BUG_ON(!tbl);
> >>>> +	mutex_lock(&container->lock);
> >>>> +	pr_debug("tce_vfio: Attaching group #%u to iommu %p\n",
> >>>> +			iommu_group_id(iommu_group), iommu_group);
> >>>> +	if (container->tbl) {
> >>>> +		printk(KERN_WARNING "tce_vfio: Only one group per IOMMU container is allowed, existing id=%d, attaching id=%d\n",
> >>>
> >>> pr_warn
> >>>
> >>>> +				iommu_group_id(container->tbl->it_group),
> >>>> +				iommu_group_id(iommu_group));
> >>>> +		mutex_unlock(&container->lock);
> >>>> +		return -EBUSY;
> >>>> +	}
> >>>> +
> >>>> +	container->tbl = tbl;
> >>>
> >>> Would it be too much paranoia to clear all the tce here as you do below
> >>> on detach?
> >>
> >> Guess so. I do unmap on detach() and the guest calls put_tce(0) (i.e.
> >> unmaps) the whole DMA window at the boot time.
> >
> > But that's just one user of this interface, we can't assume they'll all
> > be so agreeable.  If any tces were enabled here, a malicious user would
> > have a window to host memory, right?  Thanks,
> 
> 
> But I still release pages on detach(), how can this code be not called on 
> the guest exit (normal or crashed)?

What's the initial state?  You leave it clean, but who came before you?
Thanks,

Alex