Re: [PATCH v2] SUPPORT.md: extend security support for x86 hosts to 12 TiB of memory

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 25/05/2022 10:21, Jan Beulich wrote:
> c49ee0329ff3 ("SUPPORT.md: limit security support for hosts with very
> much memory"), as a result of XSA-385, restricted security support to
> 8 TiB of host memory. While subsequently further restricted for Arm,
> extend this to 12 TiB on x86, putting in place a guest restriction to
> 8 TiB (or yet less for Arm) in exchange.
>
> A 12 TiB x86 host was certified successfully for use with Xen 4.14 as
> per https://www.suse.com/nbswebapp/yesBulletin.jsp?bulletinNumber=150753.
> This in particular included running as many guests (2 TiB each) as
> possible in parallel, to actually prove that all the memory can be used
> like this. It may be relevant to note that the Optane memory there was
> used in memory-only mode, with DRAM acting as cache.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: Rebase over new host limits for Arm. Refine new guest values for
>      Arm.
>
> --- a/SUPPORT.md
> +++ b/SUPPORT.md
> @@ -50,7 +50,7 @@ For the Cortex A57 r0p0 - r1p1, see Erra
>   
>   ### Physical Memory
>   
> -    Status, x86: Supported up to 8 TiB. Hosts with more memory are supported, but not security supported.
> +    Status, x86: Supported up to 12 TiB. Hosts with more memory are supported, 
> but not security supported.
>       Status, Arm32: Supported up to 12 GiB
>       Status, Arm64: Supported up to 2 TiB
>   
> @@ -121,6 +121,17 @@ ARM only has one guest type at the momen
>   
>       Status: Supported
>   
> +## Guest Limits
> +
> +### Memory
> +
> +    Status, x86: Supported up to 8 TiB
> +    Status, Arm64: Supported up to 1 TiB
> +    Status, Arm32: Supported up to 32 GiB
IIRC, the max the architecture would allow us is 16 Gib. Here we are 
limited with how much physical memory is supported by Xen. So this wants 
to be 12 GiB.

> +
> +Guests with more memory, but less than 16 TiB, are supported,
> +but not security supported.
On Arm32, we definitely can't support up to 16 TiB. On Arm64, we would 
need some work to support it. So I would move this sentence in the 
"Status, x86" section.
Cheers,

--
Julien Grall