[PATCH v2] powerpc/book3s64/radix: Add kernel command line option to disable radix GTSE

[Bharata B Rao]

On Mon, Jul 27, 2020 at 02:29:08PM +0530, Aneesh Kumar K.V wrote:
> This adds a kernel command line option that can be used to disable GTSE support.
> Disabling GTSE implies kernel will make hcalls to invalidate TLB entries.
> 
> This was done so that we can do VM migration between configs that enable/disable
> GTSE support via hypervisor. To migrate a VM from a system that supports
> GTSE to a system that doesn't, we can boot the guest with
> radix_hcall_invalidate=on, thereby forcing the guest to use hcalls for TLB
> invalidates.
> 
> The check for hcall availability is done in pSeries_setup_arch so that
> the panic message appears on the console. This should only happen on
> a hypervisor that doesn't force the guest to hash translation even
> though it can't handle the radix GTSE=0 request via CAS. With
> radix_hcall_invalidate=on if the hypervisor doesn't support hcall_rpt_invalidate
> hcall it should force the LPAR to hash translation.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>

Tested

1. radix_hcall_invalidate=on with KVM implementation of H_RPT_INVALIDATE hcall,
   the tlb flush calls get off-loaded to the hcall.
2. radix_hcall_invalidate=on w/o H_RPT_INVALIDATE hcall, the guest kernel
   panics as per design.

Tested-by: Bharata B Rao <bharata at linux.ibm.com>