Hi,
On 11/27/19 6:25 PM, Andre Przywara wrote:
> On Mon, 25 Nov 2019 10:30:21 +0000
> Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote:
>
> Hi,
>
>> According to the PCI local bus specification [1], a device's memory size
>> must be a power of two. This is also implicit in the mechanism that a CPU
>> uses to get the memory size requirement for a PCI device.
>>
>> The vesa device requests a memory size that isn't a power of two.
>> According to the same spec [1], a device is allowed to consume more memory
>> than it actually requires. As a result, the amount of memory that the vesa
>> device now reserves has been increased.
>>
>> To prevent slip-ups in the future, a few BUILD_BUG_ON statements were added
>> in places where the memory size is known at compile time.
>>
>> [1] PCI Local Bus Specification Revision 3.0, section 6.2.5.1
>>
>> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
>> ---
>> hw/vesa.c | 2 ++
>> include/kvm/util.h | 2 ++
>> include/kvm/vesa.h | 6 +++++-
>> vfio/pci.c | 5 +++++
>> virtio/pci.c | 3 +++
>> 5 files changed, 17 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/vesa.c b/hw/vesa.c
>> index f3c5114cf4fe..75670a51be5f 100644
>> --- a/hw/vesa.c
>> +++ b/hw/vesa.c
>> @@ -58,6 +58,8 @@ struct framebuffer *vesa__init(struct kvm *kvm)
>> char *mem;
>> int r;
>>
>> + BUILD_BUG_ON(!is_power_of_two(VESA_MEM_SIZE));
>> +
>> if (!kvm->cfg.vnc && !kvm->cfg.sdl && !kvm->cfg.gtk)
>> return NULL;
>>
>> diff --git a/include/kvm/util.h b/include/kvm/util.h
>> index 4ca7aa9392b6..e90f1c2db39f 100644
>> --- a/include/kvm/util.h
>> +++ b/include/kvm/util.h
>> @@ -104,6 +104,8 @@ static inline unsigned long roundup_pow_of_two(unsigned long x)
>> return x ? 1UL << fls_long(x - 1) : 0;
>> }
>>
>> +#define is_power_of_two(x) ((x) ? ((x) & ((x) - 1)) == 0 : 0)
> This gives weird results for negative values (which the kernel avoids by having this a static inline and using an unsigned type).
> Not sure we care, but maybe (x > 0) ? ... would fix this?
Good point, I will fix it by changing the implicit comparison against 0 at the
beginning with (x) > 0.
>
>> +
>> struct kvm;
>> void *mmap_hugetlbfs(struct kvm *kvm, const char *htlbfs_path, u64 size);
>> void *mmap_anon_or_hugetlbfs(struct kvm *kvm, const char *hugetlbfs_path, u64 size);
>> diff --git a/include/kvm/vesa.h b/include/kvm/vesa.h
>> index 0fac11ab5a9f..e7d971343642 100644
>> --- a/include/kvm/vesa.h
>> +++ b/include/kvm/vesa.h
>> @@ -5,8 +5,12 @@
>> #define VESA_HEIGHT 480
>>
>> #define VESA_MEM_ADDR 0xd0000000
>> -#define VESA_MEM_SIZE (4*VESA_WIDTH*VESA_HEIGHT)
>> #define VESA_BPP 32
>> +/*
>> + * We actually only need VESA_BPP/8*VESA_WIDTH*VESA_HEIGHT bytes. But the memory
>> + * size must be a power of 2, so we round up.
>> + */
>> +#define VESA_MEM_SIZE (1 << 21)
> I don't think it's worth calculating the value and rounding it up, but can we have a BUILD_BUG checking that VESA_MEM_SIZE is big enough to hold the framebuffer?
I'm not sure what you mean. The current value of VESA_MEM_SIZE is not a power of
two, which breaks the spec. That's the reason for changing it. Are you suggesting
that we keep VESA_MEM_SIZE = 1 << 21, we remove the power_of_two check and add a
BUILD_BUG on VESA_MEM_SIZE < 4 * VESA_WIDTH * VESA_HEIGHT?
Thanks,
Alex
>
> Cheers,
> Andre
>
>>
>> struct kvm;
>> struct biosregs;
>> diff --git a/vfio/pci.c b/vfio/pci.c
>> index 76e24c156906..914732cc6897 100644
>> --- a/vfio/pci.c
>> +++ b/vfio/pci.c
>> @@ -831,6 +831,11 @@ static int vfio_pci_configure_bar(struct kvm *kvm, struct vfio_device *vdev,
>> /* Ignore invalid or unimplemented regions */
>> if (!region->info.size)
>> return 0;
>> + if (!is_power_of_two(region->info.size)) {
>> + vfio_dev_err(vdev, "region is not power of two: 0x%llx",
>> + region->info.size);
>> + return -EINVAL;
>> + }
>>
>> if (pdev->irq_modes & VFIO_PCI_IRQ_MODE_MSIX) {
>> /* Trap and emulate MSI-X table */
>> diff --git a/virtio/pci.c b/virtio/pci.c
>> index 99653cad2c0f..04e801827df9 100644
>> --- a/virtio/pci.c
>> +++ b/virtio/pci.c
>> @@ -435,6 +435,9 @@ int virtio_pci__init(struct kvm *kvm, void *dev, struct virtio_device *vdev,
>> vpci->kvm = kvm;
>> vpci->dev = dev;
>>
>> + BUILD_BUG_ON(!is_power_of_two(IOPORT_SIZE));
>> + BUILD_BUG_ON(!is_power_of_two(PCI_IO_SIZE));
>> +
>> r = ioport__register(kvm, IOPORT_EMPTY, &virtio_pci__io_ops, IOPORT_SIZE, vdev);
>> if (r < 0)
>> return r;
