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Message-ID: <20130627074501.GC5489@redhat.com>
Date: Thu, 27 Jun 2013 10:45:01 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Hans J. Koch" <hjk@...sjkoch.de>, Rob Landley <rob@...dley.net>,
linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH] uio: uio_pci_generic: Add support for MSI interrupts
On Wed, Jun 26, 2013 at 03:30:23PM -0700, Guenter Roeck wrote:
> Enable support for MSI interrupts if the device supports it.
> Since MSI interrupts are edge triggered, it is no longer necessary to
> disable interrupts in the kernel and re-enable them from user-space.
> Instead, clearing the interrupt condition in the user space application
> automatically re-enables the interrupt.
>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> An open question is if we can just do this unconditionally
> or if there should be some flag to enable it. A module parameter, maybe ?
NACK
UIO is for devices that don't do memory writes.
Anything that can do writes must be protected by an IOMMU
and/or have a secure kernel driver, not a UIO stub.
MSI is done by memory writes so if userspace
controls the device it can trick it to write
anywhere in memory.
> Documentation/DocBook/uio-howto.tmpl | 23 ++++++++++++++++++++---
> drivers/uio/uio_pci_generic.c | 15 ++++++++++++---
> 2 files changed, 32 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl
> index 9561815..69b54e0 100644
> --- a/Documentation/DocBook/uio-howto.tmpl
> +++ b/Documentation/DocBook/uio-howto.tmpl
> @@ -46,6 +46,12 @@ GPL version 2.
>
> <revhistory>
> <revision>
> + <revnumber>0.10</revnumber>
> + <date>2013-06-26</date>
> + <authorinitials>gr</authorinitials>
> + <revremark>Added MSI support to uio_pci_generic.</revremark>
> + </revision>
> + <revision>
> <revnumber>0.9</revnumber>
> <date>2009-07-16</date>
> <authorinitials>mst</authorinitials>
> @@ -935,15 +941,26 @@ and look in the output for failure reasons
> <sect1 id="uio_pci_generic_internals">
> <title>Things to know about uio_pci_generic</title>
> <para>
> -Interrupts are handled using the Interrupt Disable bit in the PCI command
> +Interrupts are handled either as MSI interrupts (if the device supports it) or
> +as legacy INTx interrupts.
> + </para>
> + <para>
> +uio_pci_generic automatically configures a device to use MSI interrupts
> +if the device supports it. If an MSI interrupt is received, the user space
> +driver is notified. Since MSI interrupts are edge sensitive, the user space
> +driver needs to clear the interrupt condition in the device before blocking
> +and waiting for more interrupts.
> + </para>
> + <para>
> +Legacy interrupts are handled using the Interrupt Disable bit in the PCI command
> register and Interrupt Status bit in the PCI status register. All devices
> compliant to PCI 2.3 (circa 2002) and all compliant PCI Express devices should
> support these bits. uio_pci_generic detects this support, and won't bind to
> devices which do not support the Interrupt Disable Bit in the command register.
> </para>
> <para>
> -On each interrupt, uio_pci_generic sets the Interrupt Disable bit.
> -This prevents the device from generating further interrupts
> +If legacy interrupts are used, uio_pci_generic sets the Interrupt Disable bit on
> +each interrupt. This prevents the device from generating further interrupts
> until the bit is cleared. The userspace driver should clear this
> bit before blocking and waiting for more interrupts.
> </para>
> diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
> index 14aa10c..3366fdb 100644
> --- a/drivers/uio/uio_pci_generic.c
> +++ b/drivers/uio/uio_pci_generic.c
> @@ -32,6 +32,7 @@
> struct uio_pci_generic_dev {
> struct uio_info info;
> struct pci_dev *pdev;
> + bool have_msi;
> };
>
> static inline struct uio_pci_generic_dev *
> @@ -46,7 +47,7 @@ static irqreturn_t irqhandler(int irq, struct uio_info *info)
> {
> struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
>
> - if (!pci_check_and_mask_intx(gdev->pdev))
> + if (!gdev->have_msi && !pci_check_and_mask_intx(gdev->pdev))
> return IRQ_NONE;
>
> /* UIO core will signal the user process. */
> @@ -58,6 +59,7 @@ static int probe(struct pci_dev *pdev,
> {
> struct uio_pci_generic_dev *gdev;
> int err;
> + bool have_msi = false;
>
> err = pci_enable_device(pdev);
> if (err) {
> @@ -73,7 +75,9 @@ static int probe(struct pci_dev *pdev,
> return -ENODEV;
> }
>
> - if (!pci_intx_mask_supported(pdev)) {
> + if (!pci_enable_msi(pdev)) {
> + have_msi = true;
> + } else if (!pci_intx_mask_supported(pdev)) {
> err = -ENODEV;
> goto err_verify;
> }
> @@ -84,10 +88,11 @@ static int probe(struct pci_dev *pdev,
> goto err_alloc;
> }
>
> + gdev->have_msi = have_msi;
> gdev->info.name = "uio_pci_generic";
> gdev->info.version = DRIVER_VERSION;
> gdev->info.irq = pdev->irq;
> - gdev->info.irq_flags = IRQF_SHARED;
> + gdev->info.irq_flags = have_msi ? 0 : IRQF_SHARED;
> gdev->info.handler = irqhandler;
> gdev->pdev = pdev;
>
> @@ -99,6 +104,8 @@ static int probe(struct pci_dev *pdev,
> err_register:
> kfree(gdev);
> err_alloc:
> + if (have_msi)
> + pci_disable_msi(pdev);
> err_verify:
> pci_disable_device(pdev);
> return err;
> @@ -109,6 +116,8 @@ static void remove(struct pci_dev *pdev)
> struct uio_pci_generic_dev *gdev = pci_get_drvdata(pdev);
>
> uio_unregister_device(&gdev->info);
> + if (gdev->have_msi)
> + pci_disable_msi(pdev);
> pci_disable_device(pdev);
> kfree(gdev);
> }
> --
> 1.7.9.5
--
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