| Message ID | 20250115101125.526492-1-ben.dooks@codethink.co.uk (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [kvmtool] kvmtool: virtio: fix endian for big endian hosts | expand |
On Wed, Jan 15, 2025 at 10:11:25AM +0000, Ben Dooks wrote: > When running on a big endian host, the virtio mmio-modern.c correctly > sets all reads to return little endian values. However the header uses > a 4 byte char for the magic value, which is always going to be in the > correct endian regardless of host endian. > > To make the simplest change, simply avoid endian convresion of the > read of the magic value. This fixes the following bug from the guest: > > [ 0.592838] virtio-mmio 10020000.virtio: Wrong magic value 0x76697274! > > Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk> > --- > virtio/mmio-modern.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/virtio/mmio-modern.c b/virtio/mmio-modern.c > index 6c0bb38..fd9c0cb 100644 > --- a/virtio/mmio-modern.c > +++ b/virtio/mmio-modern.c > @@ -66,7 +66,10 @@ static void virtio_mmio_config_in(struct kvm_cpu *vcpu, > return; > } > > - *data = cpu_to_le32(val); > + if (addr != VIRTIO_MMIO_MAGIC_VALUE) > + *data = cpu_to_le32(val); > + else > + *data = val; > } > > static void virtio_mmio_config_out(struct kvm_cpu *vcpu, > -- > 2.37.2.352.g3c44437643 > I think vendor_id should also have the same issue, but drivers don't notice because they all use VIRTIO_DEV_ANY_ID. So how about the change below instead? Thanks, drew diff --git a/include/kvm/virtio-mmio.h b/include/kvm/virtio-mmio.h index b428b8d32f48..133817c1dc44 100644 --- a/include/kvm/virtio-mmio.h +++ b/include/kvm/virtio-mmio.h @@ -18,7 +18,7 @@ struct virtio_mmio_ioevent_param { }; struct virtio_mmio_hdr { - char magic[4]; + u32 magic; u32 version; u32 device_id; u32 vendor_id; diff --git a/virtio/mmio.c b/virtio/mmio.c index fae73b52dae0..782268e8f842 100644 --- a/virtio/mmio.c +++ b/virtio/mmio.c @@ -6,6 +6,7 @@ #include "kvm/irq.h" #include "kvm/fdt.h" +#include <linux/byteorder.h> #include <linux/virtio_mmio.h> #include <string.h> @@ -168,10 +169,10 @@ int virtio_mmio_init(struct kvm *kvm, void *dev, struct virtio_device *vdev, return r; vmmio->hdr = (struct virtio_mmio_hdr) { - .magic = {'v', 'i', 'r', 't'}, + .magic = le32_to_cpu(0x74726976), /* 'virt' */ .version = legacy ? 1 : 2, .device_id = subsys_id, - .vendor_id = 0x4d564b4c , /* 'LKVM' */ + .vendor_id = le32_to_cpu(0x4d564b4c), /* 'LKVM' */ .queue_num_max = 256, };
diff --git a/virtio/mmio-modern.c b/virtio/mmio-modern.c index 6c0bb38..fd9c0cb 100644 --- a/virtio/mmio-modern.c +++ b/virtio/mmio-modern.c @@ -66,7 +66,10 @@ static void virtio_mmio_config_in(struct kvm_cpu *vcpu, return; } - *data = cpu_to_le32(val); + if (addr != VIRTIO_MMIO_MAGIC_VALUE) + *data = cpu_to_le32(val); + else + *data = val; } static void virtio_mmio_config_out(struct kvm_cpu *vcpu,
When running on a big endian host, the virtio mmio-modern.c correctly sets all reads to return little endian values. However the header uses a 4 byte char for the magic value, which is always going to be in the correct endian regardless of host endian. To make the simplest change, simply avoid endian convresion of the read of the magic value. This fixes the following bug from the guest: [ 0.592838] virtio-mmio 10020000.virtio: Wrong magic value 0x76697274! Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk> --- virtio/mmio-modern.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)