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Date: Wed, 10 Jan 2024 03:01:48 -0500
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Zheyun Shen <szy0127@sjtu.edu.cn>
Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux.dev,
	david <david@redhat.com>, jasowang@redhat.com,
	xuanzhuo@linux.alibaba.com
Subject: Re: [PATCH] driver/virtio: Add Memory Balloon Support for SEV/SEV-ES
Message-ID: <20240110025544-mutt-send-email-mst@kernel.org>
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On Wed, Jan 10, 2024 at 02:22:42PM +0800, Zheyun Shen wrote:
> For now, SEV pins guest's memory to avoid swapping or
> moving ciphertext, but leading to the inhibition of
> Memory Ballooning.
> 
> In Memory Ballooning, only guest's free pages will be relocated
> in balloon inflation and deflation, so the difference of plaintext
> doesn't matter to guest.
> 
> Memory Ballooning is a nice memory overcommitment technology can
> be used in CVM based on SEV and SEV-ES, so userspace tools can
> provide an option to allow SEV not to pin memory and enable 
> Memory Ballooning. Guest kernel may not inhibit Balloon and 
> should set shared memory for Balloon decrypted.
> 
> Signed-off-by: Zheyun Shen <szy0127@sjtu.edu.cn>

Sorry I don't get what you are saying at all.
Please format the commit log along the following lines:

Currently .....
This is bad because ...
To fix ...
As a result ...


> ---
>  drivers/virtio/virtio_balloon.c | 18 ++++++++++++++++++
>  drivers/virtio/virtio_ring.c    |  7 +++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 1fe93e93f..aca4c8a58 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -18,6 +18,9 @@
>  #include <linux/wait.h>
>  #include <linux/mm.h>
>  #include <linux/page_reporting.h>
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +#include <linux/set_memory.h>
> +#endif
>  
>  /*
>   * Balloon device works in 4K page units.  So each page is pointed to by
> @@ -870,6 +873,9 @@ static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
>  static int virtballoon_probe(struct virtio_device *vdev)
>  {
>          struct virtio_balloon *vb;
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +        size_t vb_size = PAGE_ALIGN(sizeof(*vb));
> +#endif
>          int err;
>  
>          if (!vdev->config->get) {
> @@ -878,11 +884,19 @@ static int virtballoon_probe(struct virtio_device *vdev)
>                  return -EINVAL;
>          }
>  
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +        vdev->priv = vb = kzalloc(vb_size, GFP_KERNEL);
> +#else
>          vdev->priv = vb = kzalloc(sizeof(*vb), GFP_KERNEL);
> +#endif
>          if (!vb) {
>                  err = -ENOMEM;
>                  goto out;
>          }
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +        set_memory_decrypted((unsigned long)vb, vb_size / PAGE_SIZE);
> +        memset(vb, 0, vb_size);
> +#endif
>  
>          INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
>          INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
> @@ -1101,7 +1115,11 @@ static int virtballoon_validate(struct virtio_device *vdev)
>          else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))
>                  __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
>  
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +        __virtio_set_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
> +#else
>          __virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
> +#endif
>          return 0;
>  }
>  
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 49299b1f9..875612a2e 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -14,6 +14,9 @@
>  #include <linux/kmsan.h>
>  #include <linux/spinlock.h>
>  #include <xen/xen.h>
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +#include <linux/set_memory.h>
> +#endif
>  
>  #ifdef DEBUG
>  /* For development, we want to crash whenever the ring is screwed. */
> @@ -321,6 +324,10 @@ static void *vring_alloc_queue(struct virtio_device *vdev, size_t size,
>                  if (queue) {
>                          phys_addr_t phys_addr = virt_to_phys(queue);
>                          *dma_handle = (dma_addr_t)phys_addr;
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +                        set_memory_decrypted((unsigned long)queue, PAGE_ALIGN(size) / PAGE_SIZE);
> +                        memset(queue, 0, PAGE_ALIGN(size));
> +#endif
>  
>                          /*
>                           * Sanity check: make sure we dind't truncate

No way I am going to spead CONFIG_AMD_MEM_ENCRYPT all over the place
like this.


> --
> 2.34.1