vfio/pci: implement huge_fault support

vfio/pci: implement huge_fault support

With the addition of pfnmap support in vmf_insert_pfn_{pmd,pud}() we can
take advantage of PMD and PUD faults to PCI BAR mmaps and create more
efficient mappings.  PCI BARs are always a power of two and will typically
get at least PMD alignment without userspace even trying.  Userspace
alignment for PUD mappings is also not too difficult.

Consolidate faults through a single handler with a new wrapper for
standard single page faults.  The pre-faulting behavior of commit
d71a989cf5d9 ("vfio/pci: Insert full vma on mmap'd MMIO fault") is removed
in this refactoring since huge_fault will cover the bulk of the faults and
results in more efficient page table usage.  We also want to avoid that
pre-faulted single page mappings preempt huge page mappings.

Link: https://lkml.kernel.org/r/20240826204353.2228736-20-peterx@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gavin Shan <gshan@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>