Re: [PATCH kvmtool v4 1/3] aarch64: Add stolen time support

[Sebastian Ene <sebastianene@google.com>]

On Fri, Feb 25, 2022 at 11:55:03AM +0000, Alexandru Elisei wrote:
> Hi,
> 

Hi,

> On Thu, Feb 24, 2022 at 04:51:03PM +0000, Sebastian Ene 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@google.com>
> > ---
> >  Makefile                               |  1 +
> >  arm/aarch64/arm-cpu.c                  |  1 +
> >  arm/aarch64/include/kvm/kvm-cpu-arch.h |  1 +
> >  arm/aarch64/pvtime.c                   | 94 ++++++++++++++++++++++++++
> >  arm/include/arm-common/kvm-arch.h      |  6 +-
> >  include/kvm/kvm-config.h               |  1 +
> >  6 files changed, 103 insertions(+), 1 deletion(-)
> >  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..326fb20 100644
> > --- a/arm/aarch64/arm-cpu.c
> > +++ b/arm/aarch64/arm-cpu.c
> > @@ -22,6 +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;
> > +	kvm_cpu__setup_pvtime(vcpu);
> >  	return 0;
> >  }
> >  
> > diff --git a/arm/aarch64/include/kvm/kvm-cpu-arch.h b/arm/aarch64/include/kvm/kvm-cpu-arch.h
> > index 8dfb82e..b57d6e6 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);
> > +void 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..8251f6a
> > --- /dev/null
> > +++ b/arm/aarch64/pvtime.c
> > @@ -0,0 +1,94 @@
> > +#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;
> > +};
> > +
> > +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,
> > +		   MAP_ANON_NORESERVE, -1, 0);
> > +	if (mem == MAP_FAILED)
> > +		return -ENOMEM;
> 
> Hm... man 2 mmap lists a few dozen error codes, why use -ENOMEM here instead of
> -errno? This just makes debugging harder.
> 

I will return the -errno error code here.

> > +
> > +	ret = kvm__register_dev_mem(kvm, ARM_PVTIME_MMIO_BASE,
> > +				    ARM_PVTIME_MMIO_SIZE, mem);
> > +	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;
> > +}
> > +
> > +void kvm_cpu__setup_pvtime(struct kvm_cpu *vcpu)
> > +{
> > +	int ret;
> > +	u64 pvtime_guest_addr = ARM_PVTIME_MMIO_BASE + vcpu->cpu_id *
> 
> That's trange, cpu_id is not initialized here because target->init() is called
> before setting up the cpu_id. The following patch in the series, "aarch64:
> Populate the vCPU struct before target->init()" should come before this one.
> 
> > +		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
> > +	};
> > +
> > +	BUG_ON(!vcpu);
> > +	BUG_ON(!vcpu->kvm);
> > +
> > +	kvm_cfg = &vcpu->kvm->cfg;
> > +	if (kvm_cfg && kvm_cfg->no_pvtime)
> 
> If you move the next patch in the series before this one, all the above checks
> will not be needed and should be removed.
> 
> In general, each patch in a series should be able to build properly and run a VM
> without errors. This is to help users when bisecting [1]. If I build kvmtool
> from this patch and I try to run a VM I get the error:
> 
> Error: BUG at arm/aarch64/pvtime.c:65
> 
> [1] https://github.com/torvalds/linux/blob/master/Documentation/process/submitting-patches.rst#separate-your-changes
> 

I will move the patch that handles the structure initialisation before
this one and I will remove those checks. Thanks for the suggestion !

> > +		return;
> > +
> > +	if (!pvtime_data.is_supported)
> > +		return;
> > +
> > +	ret = ioctl(vcpu->vcpu_fd, KVM_HAS_DEVICE_ATTR, &pvtime_attr);
> > +	if (ret)
> > +		goto out_err;
> 
> You should check that pvtime is supported by checking the KVM_CAP_STEAL_TIME on
> the VM fd, as that's how capabilities are advertised by KVM.
> 

I thought that it is sufficient to verify that it has the device
attributes for *PVTIME. I will add this check too, thanks for the
suggestion !

> > +
> > +	if (!pvtime_data.usr_mem) {
> > +		ret = pvtime__alloc_region(vcpu->kvm);
> 
> pvtime__alloc_region() can fail pretty catastrophically, is it ok to ignore it
> and go on? I would have expected kvm_cpu__setup_pvtime() to return an error
> which is then propagated to target->init().
>

Hmm, I didn't propagate the error code from kvm_cpu__setup_pvtime()
because if this feature is not supported it will hit:"Unable to
initialise vcpu".

But I guess that now we can propagate the error code as we have '--no-pvtime'
command argument. What do you think ?

> > +		if (ret)
> > +			goto out_err;
> > +	}
> > +
> > +	pvtime_attr.addr = (u64)&pvtime_guest_addr;
> > +	ret = ioctl(vcpu->vcpu_fd, KVM_SET_DEVICE_ATTR, &pvtime_attr);
> > +	if (!ret)
> > +		return;
> > +
> > +	pvtime__teardown_region(vcpu->kvm);
> > +out_err:
> > +	pvtime_data.is_supported = false;
> > +}
> > +
> > +dev_exit(pvtime__teardown_region);
> 
> It is customary to put the dev_exit() exactly after the function it refers to.
> 

I will move this.

> > 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
> 
> This looks good.
> 
> Thanks,
> Alex
>

Thanks for the review,
Sebastian

> > +
> >  #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
> > -- 
> > 2.35.1.473.g83b2b277ed-goog
> > 
> > _______________________________________________
> > kvmarm mailing list
> > kvmarm@lists.cs.columbia.edu
> > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm