Re: [PATCH 09/12] KVM: PPC: Book3S HV nestedv2: Do not call H_COPY_TOFROM_GUEST

["Aneesh Kumar K.V" <aneesh.kumar@kernel.org>]

On 12/11/23 9:26 AM, Vaibhav Jain wrote:
> Hi Aneesh,
> 
> Thanks for looking into this patch. My responses inline:
> 
> "Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org> writes:
> 
> <snip>
>> May be we should use 
>> firmware_has_feature(FW_FEATURE_H_COPY_TOFROM_GUEST))?
>> 
>> the nestedv2 can end up using the above hcall if it is supported by
>> the hypervisor right? In its absence we will have to translate the
>> guest ea using xlate and then use kvm_guest_read to read location
>> using the guest real address right? That xlate will also involves
>> multiple kvm_guest_read.
>> 
>> 
> Yes, Agreed and thats a nice suggestion. However ATM the hypervisor 
> supporting Nestedv2 doesnt have support for this hcall. In future
> once we have support for this hcall for nestedv2 from the hypervisor
> we can replace this branch with a firmware_has_feature() test.
> 

What I am suggesting is we convert that conditional to firmware_has_feature so that
later when hypervisor supports this hcall all older kernel can make
use of the copy_tofrom_guest without any code change.

>>> Signed-off-by: Jordan Niethe <jniethe5@gmail.com> --- 
>>> arch/powerpc/kvm/book3s_64_mmu_radix.c | 3 +++ 1 file changed, 3
>>> insertions(+)
>>> 
>>> diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c
>>> b/arch/powerpc/kvm/book3s_64_mmu_radix.c index
>>> 916af6c153a5..4a1abb9f7c05 100644 ---
>>> a/arch/powerpc/kvm/book3s_64_mmu_radix.c +++
>>> b/arch/powerpc/kvm/book3s_64_mmu_radix.c @@ -40,6 +40,9 @@
>>> unsigned long __kvmhv_copy_tofrom_guest_radix(int lpid, int pid, 
>>> unsigned long quadrant, ret = n; bool is_load = !!to;
>>> 
>>> +	if (kvmhv_is_nestedv2()) +		return H_UNSUPPORTED; + /* Can't
>>> access quadrants 1 or 2 in non-HV mode, call the HV to do it */ 
>>> if (kvmhv_on_pseries()) return
>>> plpar_hcall_norets(H_COPY_TOFROM_GUEST, lpid, pid, eaddr, -- 
>>> 2.42.0
>