On Fri, Jul 31, 2020 at 08:49:38PM +0200, Julia Suvorova wrote: > This feature allows MMCONFIG to be used even to access the base PCI > config space [1]. This means increased performance: one access to > MMCONFIG instead of two conventional accesses to I/O ports. > > Q35 makes no distinction in base or extended PCI config access to > MMCONFIG, MMCONFIG is always on, and in case it is is not initialized, > probing of PCI devices will fall back to normal process and use type1 > access. > > Enable the feature unconditionally. > > [1]: https://lore.kernel.org/kvm/20200730193510.578309-1-jus...@redhat.com/ > > Signed-off-by: Julia Suvorova <jus...@redhat.com> > --- > The feature is in the review phase. > > include/standard-headers/asm-x86/kvm_para.h | 1 + > target/i386/cpu.c | 3 ++- > target/i386/kvm.c | 1 + > 3 files changed, 4 insertions(+), 1 deletion(-) > > diff --git a/include/standard-headers/asm-x86/kvm_para.h > b/include/standard-headers/asm-x86/kvm_para.h > index 07877d3295..52eeba9067 100644 > --- a/include/standard-headers/asm-x86/kvm_para.h > +++ b/include/standard-headers/asm-x86/kvm_para.h > @@ -32,6 +32,7 @@ > #define KVM_FEATURE_POLL_CONTROL 12 > #define KVM_FEATURE_PV_SCHED_YIELD 13 > #define KVM_FEATURE_ASYNC_PF_INT 14 > +#define KVM_FEATURE_PCI_GO_MMCONFIG 15 > > #define KVM_HINTS_REALTIME 0 > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index 588f32e136..5509523bb3 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -810,7 +810,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = > { > "kvmclock", "kvm-nopiodelay", "kvm-mmu", "kvmclock", > "kvm-asyncpf", "kvm-steal-time", "kvm-pv-eoi", "kvm-pv-unhalt", > NULL, "kvm-pv-tlb-flush", NULL, "kvm-pv-ipi", > - "kvm-poll-control", "kvm-pv-sched-yield", NULL, NULL, > + "kvm-poll-control", "kvm-pv-sched-yield", NULL, > "kvm-pci-go-mmconfig", > NULL, NULL, NULL, NULL, > NULL, NULL, NULL, NULL, > "kvmclock-stable-bit", NULL, NULL, NULL, > @@ -4141,6 +4141,7 @@ static PropValue kvm_default_props[] = { > { "acpi", "off" }, > { "monitor", "off" }, > { "svm", "off" }, > + { "kvm-pci-go-mmconfig", "on" },
You'll need a TYPE_X86_CPU.kvm-pci-go-mmconfig=off entry in pc_compat_5_1 to keep guest ABI compatibility on older machine types. pc_compat_5_1 is introduced by https://lore.kernel.org/qemu-devel/20200728094645.272149-1-coh...@redhat.com/ ("hw: add compat machines for 5.2"). > { NULL, NULL }, > }; > > diff --git a/target/i386/kvm.c b/target/i386/kvm.c > index 6f18d940a5..0069e945e6 100644 > --- a/target/i386/kvm.c > +++ b/target/i386/kvm.c > @@ -440,6 +440,7 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, > uint32_t function, > if (!kvm_irqchip_in_kernel()) { > ret &= ~(1U << KVM_FEATURE_PV_UNHALT); > } > + ret |= 1U << KVM_FEATURE_PCI_GO_MMCONFIG; On most cases, enabling a feature unconditionally on kvm_arch_get_supported_cpuid() would be a mistake, but this flag seems to be an exception to the rule. A comment here explaining why it is really safe to enable it unconditionally would be welcome. > } else if (function == KVM_CPUID_FEATURES && reg == R_EDX) { > ret |= 1U << KVM_HINTS_REALTIME; > found = 1; > -- > 2.25.4 > -- Eduardo
