Re: [Minios-devel] [UNIKRAFT PATCH 16/22] plat/kvm: Disable D-Cache before doing any change for Arm64

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 11/8/18 9:51 AM, Wei Chen wrote:
> Disable the D-Cache before doing anything change, This will
> help us to avoid doing clean the D-Cache for changed area.
NAcked-by: Julien Grall <julien.grall@xxxxxxx>

I am pretty sure we discussed about it in the previous series. D-Cache 
disable means the cache will be bypassed. The processor may still 
speculatively load cache line behind your back.
So if you change memory with cache disable, then you need to invalidate 
the cache to ensure there are no stall data in it.
Furthermore, for data you write with cache disabled,  you need to know 
whether the cache was cleaned to PoC for the region you modify. The 
protocol you use should tell you what is the guarantee here.
If there are no guarantee, then you need to clean to PoC the region you 
are about to modify.
For instance, the Linux Image protocol will guarantee that the DTB, 
Kernel, Initramfs will be clean to PoC. The rest of the memory is unknown.
As you use ELF, I invite you to look at what are the guarantees here.

Cheers,

--
Julien Grall

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