Re: [PATCH] x86/shadow: depend on PV || HVM

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.04.2021 14:39, Andrew Cooper wrote:
> On 16/04/2021 13:32, Jan Beulich wrote:
>> With the building of guest_?.o now depending on PV or HVM, without
>> further #ifdef-ary shadow code won't link anymore when !PV && !HVM.
>> Since this isn't a useful configuration anyway, exclude shadow code from
>> being built in this case.
>>
>> Fixes: aff8bf94ce65 ("x86/shadow: only 4-level guest code needs building 
>> when !HVM")
>> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> --- a/xen/arch/x86/Kconfig
>> +++ b/xen/arch/x86/Kconfig
>> @@ -121,6 +121,7 @@ config XEN_SHSTK
>>  config SHADOW_PAGING
>>      bool "Shadow Paging"
>>      default !PV_SHIM_EXCLUSIVE
> 
> Hang on - this is bug, and is what needs dropping.
> 
> PV Shim uses Shadow, in default configurations, for L1TF protections to
> keep userspace out of the guest kernel.  Without it, the shim'd guest
> will be crashed when it writes an L1TF-vulnerable PTE.
> 
> OSSTest ought to have blocked this as a regression, but I suspect its
> not running the XTF PV guests in shim mode.

One thing at a time please - if there's an issue here, this wants
addressing in a separate change (which then also may need
backporting).

Jan