Re: Limitations for Running Xen on KVM Arm64

[Julien Grall <julien@xen.org>]

On 05/11/2025 13:39, haseeb.ashraf@siemens.com wrote:
> Hi,

Hi Haseeb,

> I have sent out a patch using IPAS2E1IS. The R version RIPAS2E1IS would only be helpful if we have to invalidate more than one page at a time and this is not possible unless a batch version of hypercall is implemented because otherwise there is only one page removed per hypercall.

I have only briefly look at your patch. You have the following loop:

     /* Invalidate stage-2 TLB entries by IPA range */
     for ( i = 0; i < page_count; i++ ) {
         flush_guest_tlb_one_s2(ipa);
         ipa += 1UL << PAGE_SHIFT;
     }

With RIPAS2E1IS, you would be able to replace this loop with a single 
instruction. This may not have any value in your setup because you are 
unmaping 4KB at the time. But there are other hypercalls (such as 
XENMEM_decrease_reservation) where you can remove larger mapping.

So I think there are some values to use the range version. Although, I 
would be fine if this is not handled in your current patch.

> Thanks again for your great suggestions. Please review my patch, you should've received an email.

I will add it in my list of reviews.

Cheers,

-- 
Julien Grall