Subject: Re: [PATCH kernel v2 3/4] powerpc/pseries/iommu: Separate FW_FEATURE_MULTITCE to put/stuff features

From: Thiago Jung Bauermann <[email-masked]>
Date: Mon, 16 Dec 2019 20:19:46 -0300

Alexey Kardashevskiy <[email-masked]> writes:

> H_PUT_TCE_INDIRECT allows packing up to 512 TCE updates into a single
> hypercall; H_STUFF_TCE can clear lots in a single hypercall too.
>
> However, unlike H_STUFF_TCE (which writes the same TCE to all entries),
> H_PUT_TCE_INDIRECT uses a 4K page with new TCEs. In a secure VM
> environment this means sharing a secure VM page with a hypervisor which
> we would rather avoid.
>
> This splits the FW_FEATURE_MULTITCE feature into FW_FEATURE_PUT_TCE_IND
> and FW_FEATURE_STUFF_TCE. "hcall-multi-tce" in
> the "/rtas/ibm,hypertas-functions" device tree property sets both;
> the "multitce=off" kernel command line parameter disables both.
>
> This should not cause behavioural change.
>
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>

Reviewed-by: Thiago Jung Bauermann <[email-masked]>
Tested-by: Thiago Jung Bauermann <[email-masked]>

-- 
Thiago Jung Bauermann
IBM Linux Technology Center