linux-kernel - Re: [PATCH] driver/virtio: Add Memory Balloon Support for SEV/SEV-ES

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Date: Thu, 11 Jan 2024 14:35:08 +0800 (CST)
From: Zheyun Shen <szy0127@...u.edu.cn>
To: Jason Wang <jasowang@...hat.com>, mst <mst@...hat.com>
Cc: linux-kernel <linux-kernel@...r.kernel.org>, 
	virtualization <virtualization@...ts.linux.dev>, 
	david <david@...hat.com>, xuanzhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH] driver/virtio: Add Memory Balloon Support for
 SEV/SEV-ES

On Wed, Jan 10, 2024 at 4:01 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> 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 ...

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

I will try to find out a solution with fewer macros and send patch V2
with a more perspicuous commit log.

On Thur, Jan 11, 2024 at 11:20 AM Jason Wang <jasowang@...hat.com> 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.

> This seems only true if the page is zeroed, is this true here?

Sorry, I cannot figure out why the pages should be zeroed. I think
both host kernel and guest kernel assume that the pages are not 
zeroed and will use kzalloc or manually zero them in real applications,
which is same as non-SEV environments. 

I have tested in SEV-ES, reclaiming memory by balloon inflation and reuse 
them after balloon deflation both works well with the patch. Hypervisor 
can normally give the reclaimed memory from one CVM to another, or give 
back to the origin CVM.