回复：[RFC PATCH v1 11/17] hw/virtio: force modern virtio for a CoVE guest

Hi Alistair,
> > + if (riscv_cove_vm_active()) {
> > + vdev->host_features |= 1ULL << VIRTIO_F_ACCESS_PLATFORM;
> > + vdev->host_features |= 1ULL << VIRTIO_F_VERSION_1;
> > + }
>
> This feels like a hack that we shouldn't need
You are right. I see that hw/core/machine.c already sets
iommu_platform=on and disable-legacy=on for all virtio devices when
machine->cgs is present. The proper fix is to implement
ConfidentialGuestSupport for CoVE and set machine->cgs, then this
patch becomes unnecessary and can be dropped entirely.
Will do that in v2.
Thanks,
Baolong
------------------------------------------------------------------
发件人：Alistair <[email protected]>
发送时间：2026年8月13日(周四) 00:32
收件人：Baolong Duan<[email protected]>; "qemu-devel"<[email protected]>
抄　送："qemu-riscv"<[email protected]>; alistair23<[email protected]>; dbarboza<[email protected]>; cxx194832<[email protected]>; "zengxiangyi.zxy"<[email protected]>
主　题：Re: [RFC PATCH v1 11/17] hw/virtio: force modern virtio for a CoVE guest
On Fri, 2026-07-31 at 11:50 +0800, Baolong Duan wrote:
> Devices have no direct access to the memory of a CoVE guest, so DMA
> has
> to be bounced through buffers that the guest shares explicitly. 
> Offer
> VIRTIO_F_ACCESS_PLATFORM unconditionally, together with
> VIRTIO_F_VERSION_1 which Linux requires whenever ACCESS_PLATFORM is
> offered.
> 
> Such a device therefore always negotiates in modern mode, so the
> legacy
> IOMMU_PLATFORM check in virtio-pci does not apply to it either.
> 
> Signed-off-by: Baolong Duan <[email protected]>
> ---
> hw/virtio/virtio-bus.c | 12 ++++++++++++
> hw/virtio/virtio-pci.c | 9 ++++++++-
> 2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
> index 9b545acda3..2e2917236f 100644
> --- a/hw/virtio/virtio-bus.c
> +++ b/hw/virtio/virtio-bus.c
> @@ -29,6 +29,7 @@
> #include "hw/virtio/virtio-bus.h"
> #include "hw/virtio/virtio.h"
> #include "system/address-spaces.h"
> +#include "hw/riscv/cove.h"
> 
> /* #define DEBUG_VIRTIO_BUS */
> 
> @@ -75,6 +76,17 @@ void virtio_bus_device_plugged(VirtIODevice *vdev,
> Error **errp)
> return;
> }
> 
> + /*
> + * Devices cannot access the memory of a CoVE guest directly, so
> all DMA
> + * has to be bounced through buffers the guest shares
> explicitly: offer
> + * VIRTIO_F_ACCESS_PLATFORM unconditionally. VIRTIO_F_VERSION_1
> has to be
> + * offered as well because Linux refuses ACCESS_PLATFORM without
> it.
> + */
> + if (riscv_cove_vm_active()) {
> + vdev->host_features |= 1ULL << VIRTIO_F_ACCESS_PLATFORM;
> + vdev->host_features |= 1ULL << VIRTIO_F_VERSION_1;
> + }
This feels like a hack that we shouldn't need
Alistair
> +
> if (klass->device_plugged != NULL) {
> klass->device_plugged(qbus->parent, &local_err);
> }
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 6f5db5fc42..b257d4a09f 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -34,6 +34,7 @@
> #include "hw/pci/msi.h"
> #include "hw/pci/msix.h"
> #include "hw/core/loader.h"
> +#include "hw/riscv/cove.h"
> #include "system/accel-irq.h"
> #include "system/kvm.h"
> #include "hw/virtio/virtio-pci.h"
> @@ -2048,7 +2049,13 @@ static void
> virtio_pci_device_plugged(DeviceState *d, Error **errp)
> return;
> }
> }
> - if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM))
> {
> + /*
> + * A CoVE guest always negotiates in modern mode:
> ACCESS_PLATFORM,
> + * which shares its feature bit with IOMMU_PLATFORM, is
> forced
> + * together with VERSION_1, so this check does not apply.
> + */
> + if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)
> &&
> + !riscv_cove_vm_active()) {
> error_setg(errp, "VIRTIO_F_IOMMU_PLATFORM was supported
> by"
> " neither legacy nor transitional device");
> return;