On Thu, Jul 30, 2020 at 10:37 PM Julia Suvorova <jusual@xxxxxxxxxx> wrote: > > Using MMCONFIG instead of I/O ports cuts the number of config space > accesses in half, which is faster on KVM and opens the door for > additional optimizations such as Vitaly's "[PATCH 0/3] KVM: x86: KVM > MEM_PCI_HOLE memory": > https://lore.kernel.org/kvm/20200728143741.2718593-1-vkuznets@xxxxxxxxxx You may use Link: tag for this. > However, this change will not bring significant performance improvement > unless it is running on x86 within a hypervisor. Moreover, allowing > MMCONFIG access for addresses < 256 can be dangerous for some devices: > see commit a0ca99096094 ("PCI x86: always use conf1 to access config > space below 256 bytes"). That is why a special feature flag is needed. > > Introduce KVM_FEATURE_PCI_GO_MMCONFIG, which can be enabled when the > configuration is known to be safe (e.g. in QEMU). ... > +static int __init kvm_pci_arch_init(void) > +{ > + if (raw_pci_ext_ops && > + kvm_para_has_feature(KVM_FEATURE_PCI_GO_MMCONFIG)) { Better to use traditional pattern, i.e. if (not_supported) return bail_out; ...do useful things... return 0; > + pr_info("PCI: Using MMCONFIG for base access\n"); > + raw_pci_ops = raw_pci_ext_ops; > + return 0; > + } > + return 1; Hmm... I don't remember what positive codes means there. Perhaps you need to return a rather error code? > +} -- With Best Regards, Andy Shevchenko
