On Mon, 23 Feb 2026 15:55:09 +0000
<ankita@nvidia.com> wrote:
> From: Ankit Agrawal <ankita@nvidia.com>
>
> The EGM region is invisible to the host Linux kernel and it does not
> manage the region. The EGM module manages the EGM memory and thus is
> responsible to clear out the region before handing out to the VM.
>
> Clear EGM region on EGM chardev open. To avoid CPU lockup logs,
> zap the region in 1G chunks.
>
> Suggested-by: Vikram Sethi <vsethi@nvidia.com>
> Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
> ---
> drivers/vfio/pci/nvgrace-gpu/egm.c | 43 ++++++++++++++++++++++++++++++
> 1 file changed, 43 insertions(+)
>
> diff --git a/drivers/vfio/pci/nvgrace-gpu/egm.c b/drivers/vfio/pci/nvgrace-gpu/egm.c
> index 5786ebe374a5..de7771a4145d 100644
> --- a/drivers/vfio/pci/nvgrace-gpu/egm.c
> +++ b/drivers/vfio/pci/nvgrace-gpu/egm.c
> @@ -15,6 +15,7 @@ static DEFINE_XARRAY(egm_chardevs);
> struct chardev {
> struct device device;
> struct cdev cdev;
> + atomic_t open_count;
> };
>
> static struct nvgrace_egm_dev *
> @@ -30,6 +31,42 @@ static int nvgrace_egm_open(struct inode *inode, struct file *file)
> {
> struct chardev *egm_chardev =
> container_of(inode->i_cdev, struct chardev, cdev);
> + struct nvgrace_egm_dev *egm_dev =
> + egm_chardev_to_nvgrace_egm_dev(egm_chardev);
> + void *memaddr;
> +
> + if (atomic_cmpxchg(&egm_chardev->open_count, 0, 1) != 0)
> + return -EBUSY;
> +
> + /*
> + * nvgrace-egm module is responsible to manage the EGM memory as
> + * the host kernel has no knowledge of it. Clear the region before
> + * handing over to userspace.
> + */
> + memaddr = memremap(egm_dev->egmphys, egm_dev->egmlength, MEMREMAP_WB);
> + if (!memaddr) {
> + atomic_dec(&egm_chardev->open_count);
> + return -ENOMEM;
> + }
> +
> + /*
> + * Clear in chunks of 1G to avoid CPU lockup logs.
> + */
> + {
> + size_t remaining = egm_dev->egmlength;
> + u8 *chunk_addr = (u8 *)memaddr;
> + size_t chunk_size;
Declare at the start of the function and remove this scope hack.
> +
> + while (remaining > 0) {
> + chunk_size = min(remaining, SZ_1G);
min_t(size_t,,);
> + memset(chunk_addr, 0, chunk_size);
> + cond_resched();
> + chunk_addr += chunk_size;
> + remaining -= chunk_size;
> + }
> + }
Aren't we going to want to do this asynchronously or run multiple
threads to avoid stalling VM launch?
> +
> + memunmap(memaddr);
>
> file->private_data = egm_chardev;
>
> @@ -38,8 +75,13 @@ static int nvgrace_egm_open(struct inode *inode, struct file *file)
>
> static int nvgrace_egm_release(struct inode *inode, struct file *file)
> {
> + struct chardev *egm_chardev =
> + container_of(inode->i_cdev, struct chardev, cdev);
> +
> file->private_data = NULL;
>
> + atomic_dec(&egm_chardev->open_count);
> +
> return 0;
> }
>
> @@ -108,6 +150,7 @@ setup_egm_chardev(struct nvgrace_egm_dev *egm_dev)
> egm_chardev->device.parent = &egm_dev->aux_dev.dev;
> cdev_init(&egm_chardev->cdev, &file_ops);
> egm_chardev->cdev.owner = THIS_MODULE;
> + atomic_set(&egm_chardev->open_count, 0);
Already zero from kzalloc. Thanks,
Alex
>
> ret = dev_set_name(&egm_chardev->device, "egm%lld", egm_dev->egmpxm);
> if (ret)