From c24c3e21e3c966a1fefc8c3beeb11a6a045ffe5c Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Fri, 8 Jul 2011 08:38:35 +0100 Subject: [PATCH] KEXEC: disconnect all PCI devices from the PCI bus on crash In the case of a crash, IOMMU DMA remapping gets turned off so that the kdump kernel may boot. However, this is warned as being dangerous in the VTD specification if a DMA transaction is in progress. Also, in the case of a crash, DMA transactions and interrupts from peripheral devices such as network cards are likely to keep coming in. Without DMA remapping enabled, the transactions will be writing over low memory, corrupting the crash state, and perhaps even the kdump reserved memory. Therefore, on the crash path, we can disconnect all PCI devices from their respective buses so that they are no longer able to be DMA busmasters. This reduces the risk of DMA transactions corrupting state (and will also reduce spurious interrupts arriving to the kdump kernel) until the kdump kernel and properly reset the PCI devices. Signed-off-by: Andrew Cooper --- xen/arch/x86/crash.c | 3 +++ xen/drivers/passthrough/pci.c | 19 +++++++++++++++++++ xen/include/xen/pci.h | 2 ++ 3 files changed, 24 insertions(+) diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c index ab18abb4d1..392c8d2395 100644 --- a/xen/arch/x86/crash.c +++ b/xen/arch/x86/crash.c @@ -28,6 +28,7 @@ #include #include #include +#include static atomic_t waiting_for_crash_ipi; static unsigned int crashing_cpu; @@ -78,6 +79,8 @@ static void nmi_shootdown_cpus(void) msecs--; } + disconnect_pci_devices(); + /* Crash shutdown any IOMMU functionality as the crashdump kernel is not * happy when booting if interrupt/dma remapping is still enabled */ iommu_crash_shutdown(); diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c index 33443e4ebf..f3e4113e54 100644 --- a/xen/drivers/passthrough/pci.c +++ b/xen/drivers/passthrough/pci.c @@ -462,6 +462,25 @@ int __init scan_pci_devices(void) return 0; } +/* Disconnect all PCI devices from the PCI buses. From the PCI spec: + * "When a 0 is written to [the COMMAND] register, the device is + * logically disconnected from the PCI bus for all accesses except + * configuration accesses. All devices are required to support + * this base level of functionality." + */ +void disconnect_pci_devices(void) +{ + struct pci_dev *pdev; + + spin_lock(&pcidevs_lock); + + list_for_each_entry ( pdev, &alldevs_list, alldevs_list ) + pci_conf_write16(pdev->bus, PCI_SLOT(pdev->devfn), + PCI_FUNC(pdev->devfn), PCI_COMMAND, 0); + + spin_unlock(&pcidevs_lock); +} + #ifdef SUPPORT_MSI_REMAPPING static void dump_pci_devices(unsigned char ch) { diff --git a/xen/include/xen/pci.h b/xen/include/xen/pci.h index 49eabbcd49..56355c79b9 100644 --- a/xen/include/xen/pci.h +++ b/xen/include/xen/pci.h @@ -92,6 +92,8 @@ int pci_add_device_ext(u8 bus, u8 devfn, struct pci_dev_info *info); struct pci_dev *pci_get_pdev(int bus, int devfn); struct pci_dev *pci_get_pdev_by_domain(struct domain *d, int bus, int devfn); +void disconnect_pci_devices(void); + uint8_t pci_conf_read8( unsigned int bus, unsigned int dev, unsigned int func, unsigned int reg); uint16_t pci_conf_read16( -- 2.30.2