On Wed, Mar 02, 2022 at 02:41:07PM +0000, Marc Zyngier wrote:
> Hi Sebastian,
>
Hello Marc,
> On Wed, 02 Mar 2022 14:07:35 +0000,
> Sebastian Ene <sebastianene@xxxxxxxxxx> wrote:
> >
> > This patch adds support for stolen time by sharing a memory region
> > with the guest which will be used by the hypervisor to store the stolen
> > time information. Reserve a 64kb MMIO memory region after the RTC peripheral
> > to be used by pvtime. The exact format of the structure stored by the
> > hypervisor is described in the ARM DEN0057A document.
> >
> > Signed-off-by: Sebastian Ene <sebastianene@xxxxxxxxxx>
> > ---
> > Makefile | 1 +
> > arm/aarch64/arm-cpu.c | 2 +-
> > arm/aarch64/include/kvm/kvm-cpu-arch.h | 1 +
> > arm/aarch64/pvtime.c | 103 +++++++++++++++++++++++++
> > arm/include/arm-common/kvm-arch.h | 6 +-
> > include/kvm/kvm-config.h | 1 +
> > 6 files changed, 112 insertions(+), 2 deletions(-)
> > create mode 100644 arm/aarch64/pvtime.c
> >
> > diff --git a/Makefile b/Makefile
> > index f251147..e9121dc 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -182,6 +182,7 @@ ifeq ($(ARCH), arm64)
> > OBJS += arm/aarch64/arm-cpu.o
> > OBJS += arm/aarch64/kvm-cpu.o
> > OBJS += arm/aarch64/kvm.o
> > + OBJS += arm/aarch64/pvtime.o
> > ARCH_INCLUDE := $(HDRS_ARM_COMMON)
> > ARCH_INCLUDE += -Iarm/aarch64/include
> >
> > diff --git a/arm/aarch64/arm-cpu.c b/arm/aarch64/arm-cpu.c
> > index d7572b7..7e4a3c1 100644
> > --- a/arm/aarch64/arm-cpu.c
> > +++ b/arm/aarch64/arm-cpu.c
> > @@ -22,7 +22,7 @@ static void generate_fdt_nodes(void *fdt, struct kvm *kvm)
> > static int arm_cpu__vcpu_init(struct kvm_cpu *vcpu)
> > {
> > vcpu->generate_fdt_nodes = generate_fdt_nodes;
> > - return 0;
> > + return kvm_cpu__setup_pvtime(vcpu);
> > }
> >
> > static struct kvm_arm_target target_generic_v8 = {
> > diff --git a/arm/aarch64/include/kvm/kvm-cpu-arch.h b/arm/aarch64/include/kvm/kvm-cpu-arch.h
> > index 8dfb82e..2b2c1ff 100644
> > --- a/arm/aarch64/include/kvm/kvm-cpu-arch.h
> > +++ b/arm/aarch64/include/kvm/kvm-cpu-arch.h
> > @@ -19,5 +19,6 @@
> >
> > void kvm_cpu__select_features(struct kvm *kvm, struct kvm_vcpu_init *init);
> > int kvm_cpu__configure_features(struct kvm_cpu *vcpu);
> > +int kvm_cpu__setup_pvtime(struct kvm_cpu *vcpu);
> >
> > #endif /* KVM__KVM_CPU_ARCH_H */
> > diff --git a/arm/aarch64/pvtime.c b/arm/aarch64/pvtime.c
> > new file mode 100644
> > index 0000000..fdde683
> > --- /dev/null
> > +++ b/arm/aarch64/pvtime.c
> > @@ -0,0 +1,103 @@
> > +#include "kvm/kvm.h"
> > +#include "kvm/kvm-cpu.h"
> > +#include "kvm/util.h"
> > +
> > +#include <linux/byteorder.h>
> > +#include <linux/types.h>
> > +
> > +#define ARM_PVTIME_STRUCT_SIZE (64)
> > +
> > +struct pvtime_data_priv {
> > + bool is_supported;
> > + char *usr_mem;
>
> Consider using void * for pointers that do not have any particular
> semantics associated to them.
>
I will update the pointer to void * type.
> > +};
> > +
> > +static struct pvtime_data_priv pvtime_data = {
> > + .is_supported = true,
> > + .usr_mem = NULL
> > +};
> > +
> > +static int pvtime__alloc_region(struct kvm *kvm)
> > +{
> > + char *mem;
> > + int ret = 0;
> > +
> > + mem = mmap(NULL, ARM_PVTIME_MMIO_SIZE, PROT_RW,
>
> I sort of object to the 'MMIO' part of the name. The spec is quite
> clear that this should be normal memory. That's purely cosmetic, but
> still a bit confusing.
>
I will remove the 'MMIO' part of the name: ARM_PVTIME_SIZE and
ARM_PVTIME_BASE will be the new definitions. Initially I thought to keep
the 'MMIO' name as this ram portion is placed after RTC_MMIO region but I
agree that it's a bit confusing.
> > + MAP_ANON_NORESERVE, -1, 0);
> > + if (mem == MAP_FAILED)
> > + return -errno;
> > +
> > + ret = kvm__register_dev_mem(kvm, ARM_PVTIME_MMIO_BASE,
> > + ARM_PVTIME_MMIO_SIZE, mem);
>
> This, on the other side, is wrong. Since the pvtime pages are memory,
> mapping them with device attributes will do the wrong thing (the
> hypervisor will write to a cacheable mapping, and the guest will
> bypass the cache due to the S2 override that you provide here).
>
> kvm__register_ram() is more likely to lead to the behaviour you'd
> expect.
>
Thanks for the explanation ! Nice catch. I will update the call and use
kvm__register_ram().
> > + if (ret) {
> > + munmap(mem, ARM_PVTIME_MMIO_SIZE);
> > + return ret;
> > + }
> > +
> > + pvtime_data.usr_mem = mem;
> > + return ret;
> > +}
> > +
> > +static int pvtime__teardown_region(struct kvm *kvm)
> > +{
> > + if (pvtime_data.usr_mem == NULL)
> > + return 0;
> > +
> > + kvm__destroy_mem(kvm, ARM_PVTIME_MMIO_BASE,
> > + ARM_PVTIME_MMIO_SIZE, pvtime_data.usr_mem);
> > + munmap(pvtime_data.usr_mem, ARM_PVTIME_MMIO_SIZE);
> > + pvtime_data.usr_mem = NULL;
> > + return 0;
> > +}
> > +
> > +dev_exit(pvtime__teardown_region);
> > +
> > +int kvm_cpu__setup_pvtime(struct kvm_cpu *vcpu)
> > +{
> > + int ret;
> > + bool has_stolen_time;
> > + u64 pvtime_guest_addr = ARM_PVTIME_MMIO_BASE + vcpu->cpu_id *
> > + ARM_PVTIME_STRUCT_SIZE;
> > + struct kvm_config *kvm_cfg = NULL;
> > + struct kvm_device_attr pvtime_attr = (struct kvm_device_attr) {
> > + .group = KVM_ARM_VCPU_PVTIME_CTRL,
> > + .addr = KVM_ARM_VCPU_PVTIME_IPA
> > + };
> > +
> > + kvm_cfg = &vcpu->kvm->cfg;
> > + if (kvm_cfg->no_pvtime)
> > + return 0;
> > +
> > + if (!pvtime_data.is_supported)
> > + return -ENOTSUP;
>
> It is a bit odd to have this hard failure if running on a system that
> doesn't have pvtime. It forces the user to alter their command-line,
> which is a bit annoying. I'd rather have a soft-fail here.
>
The flag 'is_supported' is set to false when we support pvtime but we
fail to configure it. We verify that we support pvtime by calling the check
extension KVM_CAP_STEAL_TIME. I think the naming is odd here for the
flag name. It should be : 'is_failed_cfg'.
> > +
> > + has_stolen_time = kvm__supports_extension(vcpu->kvm,
> > + KVM_CAP_STEAL_TIME);
> > + if (!has_stolen_time)
> > + return 0;
> > +
> > + ret = ioctl(vcpu->vcpu_fd, KVM_HAS_DEVICE_ATTR, &pvtime_attr);
> > + if (ret) {
> > + perror("KVM_HAS_DEVICE_ATTR failed\n");
> > + goto out_err;
> > + }
> > +
> > + if (!pvtime_data.usr_mem) {
> > + ret = pvtime__alloc_region(vcpu->kvm);
> > + if (ret) {
> > + perror("Failed allocating pvtime region\n");
> > + goto out_err;
> > + }
> > + }
> > +
> > + pvtime_attr.addr = (u64)&pvtime_guest_addr;
> > + ret = ioctl(vcpu->vcpu_fd, KVM_SET_DEVICE_ATTR, &pvtime_attr);
> > + if (!ret)
> > + return 0;
> > +
> > + perror("KVM_SET_DEVICE_ATTR failed\n");
> > + pvtime__teardown_region(vcpu->kvm);
> > +out_err:
> > + pvtime_data.is_supported = false;
> > + return ret;
> > +}
> > diff --git a/arm/include/arm-common/kvm-arch.h b/arm/include/arm-common/kvm-arch.h
> > index c645ac0..3f82663 100644
> > --- a/arm/include/arm-common/kvm-arch.h
> > +++ b/arm/include/arm-common/kvm-arch.h
> > @@ -15,7 +15,8 @@
> > * | PCI |////| plat | | | | |
> > * | I/O |////| MMIO: | Flash | virtio | GIC | PCI | DRAM
> > * | space |////| UART, | | MMIO | | (AXI) |
> > - * | |////| RTC | | | | |
> > + * | |////| RTC, | | | | |
> > + * | |////| PVTIME| | | | |
> > * +-------+----+-------+-------+--------+-----+---------+---......
> > */
> >
> > @@ -34,6 +35,9 @@
> > #define ARM_RTC_MMIO_BASE (ARM_UART_MMIO_BASE + ARM_UART_MMIO_SIZE)
> > #define ARM_RTC_MMIO_SIZE 0x10000
> >
> > +#define ARM_PVTIME_MMIO_BASE (ARM_RTC_MMIO_BASE + ARM_RTC_MMIO_SIZE)
> > +#define ARM_PVTIME_MMIO_SIZE SZ_64K
> > +
> > #define KVM_FLASH_MMIO_BASE (ARM_MMIO_AREA + 0x1000000)
> > #define KVM_FLASH_MAX_SIZE 0x1000000
> >
> > diff --git a/include/kvm/kvm-config.h b/include/kvm/kvm-config.h
> > index 6a5720c..48adf27 100644
> > --- a/include/kvm/kvm-config.h
> > +++ b/include/kvm/kvm-config.h
> > @@ -62,6 +62,7 @@ struct kvm_config {
> > bool no_dhcp;
> > bool ioport_debug;
> > bool mmio_debug;
> > + bool no_pvtime;
> > };
> >
> > #endif
>
> Thanks,
>
Thanks for the review,
> M.
>
Sebastian
> --
> Without deviation from the norm, progress is not possible.
