On Wed, Jul 22, 2020 at 11:43 AM Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote: > > Julia Suvorova <jusual@xxxxxxxxxx> writes: > > > 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. > > > > [1] https://lkml.org/lkml/2020/5/14/936 > > > > 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; > > > > return 1; > > } > > This implies mmconfig access method is always functional (when present) > for all KVM guests, regardless of hypervisor version/which KVM userspace > is is use/... In case the assumption is true the patch looks good (to > me) but in case it isn't or if we think that more control over this > is needed we may want to introduce a PV feature bit for KVM. Ok, I'll introduce a feature bit and turn it on in QEMU. > Also, I'm thinking about moving this to arch/x86/kernel/kvm.c: we can > override x86_init.pci.arch_init and reassign raw_pci_ops after doing > pci_arch_init(). This might be a good idea. Best regards, Julia Suvorova.
