With the introduction of memory I/O (MIO) instructions enbaled in commit
71ba41c9b1d9 ("s390/pci: provide support for MIO instructions") s390
gained support for direct user-space access to mapped PCI resources.
Even without those however user-space can access mapped PCI resources
via the s390 specific MMIO syscalls. There is thus nothing fundamentally
preventing s390 from supporting VFIO_PCI_MMAP allowing user-space drivers
to access PCI resources without going through the pread() interface.
To actually enable VFIO_PCI_MMAP a few issues need fixing however.
Firstly the s390 MMIO syscalls do not cause a page fault when
follow_pte() fails due to the page not being present. This breaks
vfio-pci's mmap() handling which lazily maps on first access.
Secondly on s390 there is a virtual PCI device called ISM which has
a few oddities. For one it claims to have a 256 TiB PCI BAR (not a typo)
which leads to any attempt to mmap() it fail with the following message:
vmap allocation for size 281474976714752 failed: use vmalloc=<size> to increase size
Even if one tried to map this BAR only partially the mapping would not
be usable on systems with MIO support enabled. So just block mapping
BARs which don't fit between IOREMAP_START and IOREMAP_END.
Note:
For your convenience the code is also available in the tagged and signed
b4/vfio_pci_mmap branch on my git.kernel.org site below:
https: //git.kernel.org/pub/scm/linux/kernel/git/niks/linux.git/
Thanks,
Niklas
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Niklas Schnelle <[email protected]>
---
Changes in v2:
- Changed last patch to remove VFIO_PCI_MMAP instead of just enabling it
for s390 as it is unconditionally true with s390 supporting PCI resource mmap() (Jason)
- Collected R-bs from Jason
- Link to v1: https://lore.kernel.org/r/[email protected]
---
Niklas Schnelle (3):
s390/pci: Fix s390_mmio_read/write syscall page fault handling
vfio/pci: Tolerate oversized BARs by disallowing mmap
vfio/pci: Enable PCI resource mmap() on s390 and remove VFIO_PCI_MMAP
arch/s390/pci/pci_mmio.c | 18 +++++++++++++-----
drivers/vfio/pci/Kconfig | 4 ----
drivers/vfio/pci/vfio_pci_core.c | 11 ++++++-----
3 files changed, 19 insertions(+), 14 deletions(-)
---
base-commit: a38297e3fb012ddfa7ce0321a7e5a8daeb1872b6
change-id: 20240503-vfio_pci_mmap-1549e3d02ca7
Best regards,
--
Niklas Schnelle
With the introduction of memory I/O (MIO) instructions enbaled in commit
71ba41c9b1d9 ("s390/pci: provide support for MIO instructions") s390
gained support for direct user-space access to mapped PCI resources.
Even without those however user-space can access mapped PCI resources
via the s390 specific MMIO syscalls. Thus mmap() can and should be
supported on all s390 systems with native PCI. Since VFIO_PCI_MMAP
enablement for s390 would make it unconditionally true and thus
pointless just remove it entirely.
Link: https://lore.kernel.org/all/[email protected]/
Suggested-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Niklas Schnelle <[email protected]>
---
drivers/vfio/pci/Kconfig | 4 ----
drivers/vfio/pci/vfio_pci_core.c | 3 ---
2 files changed, 7 deletions(-)
diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index 15821a2d77d2..9c88e3a6d06b 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -7,10 +7,6 @@ config VFIO_PCI_CORE
select VFIO_VIRQFD
select IRQ_BYPASS_MANAGER
-config VFIO_PCI_MMAP
- def_bool y if !S390
- depends on VFIO_PCI_CORE
-
config VFIO_PCI_INTX
def_bool y if !S390
depends on VFIO_PCI_CORE
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 23961299b695..35b8e8f214af 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -121,9 +121,6 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev)
res = &vdev->pdev->resource[bar];
- if (!IS_ENABLED(CONFIG_VFIO_PCI_MMAP))
- goto no_mmap;
-
if (!(res->flags & IORESOURCE_MEM))
goto no_mmap;
--
2.40.1
On s390 there is a virtual PCI device called ISM which has a few rather
annoying oddities. For one it claims to have a 256 TiB PCI BAR (not
a typo) which leads to any attempt to mmap() it failing during vmap.
Even if one tried to map this "BAR" only partially the mapping would not
be usable on systems with MIO support enabled however. This is because
of another oddity in that this virtual PCI device does not support the
newer memory I/O (MIO) PCI instructions and legacy PCI instructions are
not accessible by user-space when MIO is in use. If this device needs to
be accessed by user-space it will thus need a vfio-pci variant driver.
Until then work around both issues by excluding resources which don't
fit between IOREMAP_START and IOREMAP_END in vfio_pci_probe_mmaps().
Reviewed-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Niklas Schnelle <[email protected]>
---
drivers/vfio/pci/vfio_pci_core.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index d94d61b92c1a..23961299b695 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -28,6 +28,7 @@
#include <linux/nospec.h>
#include <linux/sched/mm.h>
#include <linux/iommufd.h>
+#include <linux/ioremap.h>
#if IS_ENABLED(CONFIG_EEH)
#include <asm/eeh.h>
#endif
@@ -129,9 +130,12 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev)
/*
* The PCI core shouldn't set up a resource with a
* type but zero size. But there may be bugs that
- * cause us to do that.
+ * cause us to do that. There is also at least one
+ * device which advertises a resource too large to
+ * ioremap().
*/
- if (!resource_size(res))
+ if (!resource_size(res) ||
+ resource_size(res) > (IOREMAP_END + 1 - IOREMAP_START))
goto no_mmap;
if (resource_size(res) >= PAGE_SIZE) {
--
2.40.1
On Thu, May 23, 2024 at 01:10:16PM +0200, Niklas Schnelle wrote:
> With the introduction of memory I/O (MIO) instructions enbaled in commit
> 71ba41c9b1d9 ("s390/pci: provide support for MIO instructions") s390
> gained support for direct user-space access to mapped PCI resources.
> Even without those however user-space can access mapped PCI resources
> via the s390 specific MMIO syscalls. Thus mmap() can and should be
> supported on all s390 systems with native PCI. Since VFIO_PCI_MMAP
> enablement for s390 would make it unconditionally true and thus
> pointless just remove it entirely.
>
> Link: https://lore.kernel.org/all/[email protected]/
> Suggested-by: Jason Gunthorpe <[email protected]>
> Signed-off-by: Niklas Schnelle <[email protected]>
> ---
> drivers/vfio/pci/Kconfig | 4 ----
> drivers/vfio/pci/vfio_pci_core.c | 3 ---
> 2 files changed, 7 deletions(-)
Reviewed-by: Jason Gunthorpe <[email protected]>
Jason
On 5/23/24 7:10 AM, Niklas Schnelle wrote:
> On s390 there is a virtual PCI device called ISM which has a few rather
> annoying oddities. For one it claims to have a 256 TiB PCI BAR (not
> a typo) which leads to any attempt to mmap() it failing during vmap.
>
> Even if one tried to map this "BAR" only partially the mapping would not
> be usable on systems with MIO support enabled however. This is because
> of another oddity in that this virtual PCI device does not support the
> newer memory I/O (MIO) PCI instructions and legacy PCI instructions are
> not accessible by user-space when MIO is in use. If this device needs to
> be accessed by user-space it will thus need a vfio-pci variant driver.
> Until then work around both issues by excluding resources which don't
> fit between IOREMAP_START and IOREMAP_END in vfio_pci_probe_mmaps().
>
> Reviewed-by: Jason Gunthorpe <[email protected]>
> Signed-off-by: Niklas Schnelle <[email protected]>
> ---
Reviewed-by: Matthew Rosato <[email protected]>
On 5/23/24 7:10 AM, Niklas Schnelle wrote:
> With the introduction of memory I/O (MIO) instructions enbaled in commit
> 71ba41c9b1d9 ("s390/pci: provide support for MIO instructions") s390
> gained support for direct user-space access to mapped PCI resources.
> Even without those however user-space can access mapped PCI resources
> via the s390 specific MMIO syscalls. Thus mmap() can and should be
> supported on all s390 systems with native PCI. Since VFIO_PCI_MMAP
> enablement for s390 would make it unconditionally true and thus
> pointless just remove it entirely.
>
> Link: https://lore.kernel.org/all/[email protected]/
> Suggested-by: Jason Gunthorpe <[email protected]>
> Signed-off-by: Niklas Schnelle <[email protected]>
Reviewed-by: Matthew Rosato <[email protected]>
Also sanity tested on s390 with mlx, nvme, ISM over vfio-pci (the latter of which triggers the patch 2 scenario).