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Tsirkin" To: Jason Wang Cc: virtualization , linux-kernel , "Hetzelt, Felicitas" , "kaplan, david" , Konrad Rzeszutek Wilk Subject: Re: [PATCH 7/9] virtio-pci: harden INTX interrupts Message-ID: <20210913023757-mutt-send-email-mst@kernel.org> References: <20210913055353.35219-1-jasowang@redhat.com> <20210913055353.35219-8-jasowang@redhat.com> <20210913022824-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 13, 2021 at 02:36:54PM +0800, Jason Wang wrote: > On Mon, Sep 13, 2021 at 2:33 PM Michael S. Tsirkin wrote: > > > > On Mon, Sep 13, 2021 at 01:53:51PM +0800, Jason Wang wrote: > > > This patch tries to make sure the virtio interrupt handler for INTX > > > won't be called after a reset and before virtio_device_ready(). We > > > can't use IRQF_NO_AUTOEN since we're using shared interrupt > > > (IRQF_SHARED). So this patch tracks the INTX enabling status in a new > > > intx_soft_enabled variable and toggle it during in > > > vp_disable/enable_vectors(). The INTX interrupt handler will check > > > intx_soft_enabled before processing the actual interrupt. > > > > > > Signed-off-by: Jason Wang > > > > > > Not all that excited about all the memory barriers for something > > that should be an extremely rare event (for most kernels - > > literally once per boot). Can't we do better? > > I'm not sure, but do we need to care about the slow path (INTX)? Otherwise we won't try to support this, right? > (Or do you have a better approach?) > > Thanks Don't know really, maybe rcu or whatever? But let's try to be much more specific - is there anything specific we are trying to protect against here? > > > > > --- > > > drivers/virtio/virtio_pci_common.c | 18 ++++++++++++++++-- > > > drivers/virtio/virtio_pci_common.h | 1 + > > > 2 files changed, 17 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c > > > index 0b9523e6dd39..835197151dc1 100644 > > > --- a/drivers/virtio/virtio_pci_common.c > > > +++ b/drivers/virtio/virtio_pci_common.c > > > @@ -30,8 +30,12 @@ void vp_disable_vectors(struct virtio_device *vdev) > > > struct virtio_pci_device *vp_dev = to_vp_device(vdev); > > > int i; > > > > > > - if (vp_dev->intx_enabled) > > > + if (vp_dev->intx_enabled) { > > > + vp_dev->intx_soft_enabled = false; > > > + /* ensure the vp_interrupt see this intx_soft_enabled value */ > > > + smp_wmb(); > > > synchronize_irq(vp_dev->pci_dev->irq); > > > + } > > > > > > for (i = 0; i < vp_dev->msix_vectors; ++i) > > > disable_irq(pci_irq_vector(vp_dev->pci_dev, i)); > > > @@ -43,8 +47,12 @@ void vp_enable_vectors(struct virtio_device *vdev) > > > struct virtio_pci_device *vp_dev = to_vp_device(vdev); > > > int i; > > > > > > - if (vp_dev->intx_enabled) > > > + if (vp_dev->intx_enabled) { > > > + vp_dev->intx_soft_enabled = true; > > > + /* ensure the vp_interrupt see this intx_soft_enabled value */ > > > + smp_wmb(); > > > return; > > > + } > > > > > > for (i = 0; i < vp_dev->msix_vectors; ++i) > > > enable_irq(pci_irq_vector(vp_dev->pci_dev, i)); > > > @@ -97,6 +105,12 @@ static irqreturn_t vp_interrupt(int irq, void *opaque) > > > struct virtio_pci_device *vp_dev = opaque; > > > u8 isr; > > > > > > + if (!vp_dev->intx_soft_enabled) > > > + return IRQ_NONE; > > > + > > > + /* read intx_soft_enabled before read others */ > > > + smp_rmb(); > > > + > > > /* reading the ISR has the effect of also clearing it so it's very > > > * important to save off the value. */ > > > isr = ioread8(vp_dev->isr); > > > diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h > > > index a235ce9ff6a5..3c06e0f92ee4 100644 > > > --- a/drivers/virtio/virtio_pci_common.h > > > +++ b/drivers/virtio/virtio_pci_common.h > > > @@ -64,6 +64,7 @@ struct virtio_pci_device { > > > /* MSI-X support */ > > > int msix_enabled; > > > int intx_enabled; > > > + bool intx_soft_enabled; > > > cpumask_var_t *msix_affinity_masks; > > > /* Name strings for interrupts. This size should be enough, > > > * and I'm too lazy to allocate each name separately. */ > > > -- > > > 2.25.1 > >