Re: [PATCH] KVM: allow NULL writable argument to __kvm_faultin_pfn

On Mon, Jan 06, 2025, Sean Christopherson wrote:

On Wed, Jan 01, 2025, Paolo Bonzini wrote:

quoted

kvm_follow_pfn() is able to work with NULL in the .map_writable field
of the homonymous struct.  But __kvm_faultin_pfn() rejects the combo
despite KVM for e500 trying to use it.  Indeed .map_writable is not
particularly useful if the flags include FOLL_WRITE and readonly
guest memory is not supported, so add support to __kvm_faultin_pfn()
for this case.

I would prefer to keep the sanity check to minimize the risk of a page fault
handler not supporting opportunistic write mappings.  e500 is definitely the
odd one out here.

Per a quick chat at PUCK, Paolo is going to try and fix the e500 code to actually
use the @writable param as it's intended.