On Wed, Jul 22, 2020 at 02:15:13AM +0200, Julia Suvorova wrote: > Scanning for PCI devices at boot takes a long time for KVM guests. It > can be reduced if KVM will handle all configuration space accesses for > non-existent devices without going to userspace [1]. But for this to > work, all accesses must go through MMCONFIG. > This change allows to use pci_mmcfg as raw_pci_ops for 64-bit KVM > guests making MMCONFIG the default access method. The above *looks* like it's intended to be two paragraphs, which would be easier to read with a blank line between. The last sentence should say what the patch actually *does*, e.g., "Use pci_mmcfg as raw_pci_ops ..." > [1] https://lkml.org/lkml/2020/5/14/936 Please use a lore.kernel.org URL instead because it's more usable and I'd rather depend on kernel.org than lkml.org. > Signed-off-by: Julia Suvorova <jusual@xxxxxxxxxx> > --- > arch/x86/pci/direct.c | 5 +++++ > arch/x86/pci/mmconfig_64.c | 3 +++ > 2 files changed, 8 insertions(+) > > diff --git a/arch/x86/pci/direct.c b/arch/x86/pci/direct.c > index a51074c55982..8ff6b65d8f48 100644 > --- a/arch/x86/pci/direct.c > +++ b/arch/x86/pci/direct.c > @@ -6,6 +6,7 @@ > #include <linux/pci.h> > #include <linux/init.h> > #include <linux/dmi.h> > +#include <linux/kvm_para.h> > #include <asm/pci_x86.h> > > /* > @@ -264,6 +265,10 @@ void __init pci_direct_init(int type) > { > if (type == 0) > return; > + > + if (raw_pci_ext_ops && kvm_para_available()) > + return; > printk(KERN_INFO "PCI: Using configuration type %d for base access\n", > type); > if (type == 1) { > diff --git a/arch/x86/pci/mmconfig_64.c b/arch/x86/pci/mmconfig_64.c > index 0c7b6e66c644..9eb772821766 100644 > --- a/arch/x86/pci/mmconfig_64.c > +++ b/arch/x86/pci/mmconfig_64.c > @@ -10,6 +10,7 @@ > #include <linux/init.h> > #include <linux/acpi.h> > #include <linux/bitmap.h> > +#include <linux/kvm_para.h> > #include <linux/rcupdate.h> > #include <asm/e820/api.h> > #include <asm/pci_x86.h> > @@ -122,6 +123,8 @@ int __init pci_mmcfg_arch_init(void) > } > > raw_pci_ext_ops = &pci_mmcfg; > + if (kvm_para_available()) > + raw_pci_ops = &pci_mmcfg; The idea of using MMCONFIG for *all* config space, not just extended config space, makes sense to me, although the very long discussion at https://lore.kernel.org/lkml/20071225032605.29147200@xxxxxxxxxxxxxxxxxxxxx/ makes me wary. Of course I realize you're talking specifically about KVM, not doing this in general. But it doesn't seem right to make this specific to KVM, since it's not obvious to me that there's a basis in PCI for making this distinction. > return 1; > } > -- > 2.25.4 >
