From 8fe55ef23387ce3c7488375b1fd539420d7654bb Mon Sep 17 00:00:00 2001 From: Russell King Date: Thu, 13 May 2021 15:18:27 +0100 Subject: PCI: Dynamically map ECAM regions Attempting to boot 32-bit ARM kernels under QEMU's 3.x virt models fails when we have more than 512M of RAM in the model as we run out of vmalloc space for the PCI ECAM regions. This failure will be silent when running libvirt, as the console in that situation is a PCI device. In this configuration, the kernel maps the whole ECAM, which QEMU sets up for 256 buses, even when maybe only seven buses are in use. Each bus uses 1M of ECAM space, and ioremap() adds an additional guard page between allocations. The kernel vmap allocator will align these regions to 512K, resulting in each mapping eating 1.5M of vmalloc space. This means we need 384M of vmalloc space just to map all of these, which is very wasteful of resources. Fix this by only mapping the ECAM for buses we are going to be using. In my setups, this is around seven buses in most guests, which is 10.5M of vmalloc space - way smaller than the 384M that would otherwise be required. This also means that the kernel can boot without forcing extra RAM into highmem with the vmalloc= argument, or decreasing the virtual RAM available to the guest. Suggested-by: Arnd Bergmann Link: https://lore.kernel.org/r/E1lhCAV-0002yb-50@rmk-PC.armlinux.org.uk Signed-off-by: Russell King Signed-off-by: Bjorn Helgaas Reviewed-by: Arnd Bergmann --- include/linux/pci-ecam.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/pci-ecam.h') diff --git a/include/linux/pci-ecam.h b/include/linux/pci-ecam.h index fbdadd4d8377..adea5a4771cf 100644 --- a/include/linux/pci-ecam.h +++ b/include/linux/pci-ecam.h @@ -55,6 +55,7 @@ struct pci_ecam_ops { struct pci_config_window { struct resource res; struct resource busr; + unsigned int bus_shift; void *priv; const struct pci_ecam_ops *ops; union { -- cgit v1.2.3