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 Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx> --- hw/vesa.c | 3 +++ include/kvm/util.h | 2 ++ include/kvm/vesa.h | 6 +++++- virtio/pci.c | 3 +++ 4 files changed, 13 insertions(+), 1 deletion(-) diff --git a/hw/vesa.c b/hw/vesa.c index f3c5114cf4fe..d75b4b316a1e 100644 --- a/hw/vesa.c +++ b/hw/vesa.c @@ -58,6 +58,9 @@ struct framebuffer *vesa__init(struct kvm *kvm) char *mem; int r; + BUILD_BUG_ON(!is_power_of_two(VESA_MEM_SIZE)); + BUILD_BUG_ON(VESA_MEM_SIZE < VESA_BPP/8 * VESA_WIDTH * VESA_HEIGHT); + 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..199724c4018c 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) > 0 ? ((x) & ((x) - 1)) == 0 : 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) struct kvm; struct biosregs; 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; -- 2.20.1
