KVM: X86/MMU: Use one-off local shadow page for special roots

From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

Current code uses mmu->pae_root, mmu->pml4_root, and mmu->pml5_root to
setup special roots.  The initialization code is complex and the roots
are not associated with struct kvm_mmu_page which causes the code more
complex.

So add new local shadow pages to simplify it.

The local shadow pages are associated with struct kvm_mmu_page and
VCPU-local.

The local shadow pages are created and freed when the roots are
changed (or one-off) which can be optimized but not in the patchset
since the re-creating is light way (in normal case only the struct
kvm_mmu_page needs to be re-allocated and sp->spt doens't, because
it is likely to be mmu->pae_root)

The patchset also fixes a possible bug described in:
https://lore.kernel.org/lkml/20220415103414.86555-1-jiang...
as patch1.

And the fixing is simplifed in patch9 with the help of local shadow page.

Note:
using_local_root_page() can be implemented in two ways.

static bool using_local_root_page(struct kvm_mmu *mmu)
{
	return mmu->root_role.level == PT32E_ROOT_LEVEL ||
	       (!mmu->root_role.direct && mmu->cpu_role.base.level <= PT32E_ROOT_LEVEL);
}

static bool using_local_root_page(struct kvm_mmu *mmu)
{
	if (mmu->root_role.direct)
		return mmu->root_role.level == PT32E_ROOT_LEVEL;
	else
		return mmu->cpu_role.base.level <= PT32E_ROOT_LEVEL;
}

I prefer the second way.  But when I wrote the documents for them.  I
couldn't explain well enough for the second way.  Maybe I explained the
second way in a wrong aspect or my English is not qualified to explain
it.

So I put the first way in patch 2 and the second way in patch3.
Patch3 adds much more documents and changes the first way to the second
way.  Patch3 can be discarded.

Changed from v2:
	Add document for using_local_root_page()
	Update many documents
	Address review comments
	Add a patch that fix a possible bug (and split other patches for patch9)

Changed from v1:
	Rebase to newest kvm/queue. Slightly update patch4.

[V2]: https://lore.kernel.org/lkml/20220503150735.32723-1-jiang...
[V1]: https://lore.kernel.org/lkml/20220420132605.3813-1-jiangs...


Lai Jiangshan (12):
  KVM: X86/MMU: Verify PDPTE for nested NPT in PAE paging mode when page
    fault
  KVM: X86/MMU: Add using_local_root_page()
  KVM: X86/MMU: Reduce a check in using_local_root_page() for common
    cases
  KVM: X86/MMU: Add local shadow pages
  KVM: X86/MMU: Link PAE root pagetable with its children
  KVM: X86/MMU: Activate local shadow pages and remove old logic
  KVM: X86/MMU: Remove the check of the return value of to_shadow_page()
  KVM: X86/MMU: Allocate mmu->pae_root for PAE paging on-demand
  KVM: X86/MMU: Move the verifying of NPT's PDPTE in FNAME(fetch)
  KVM: X86/MMU: Remove unused INVALID_PAE_ROOT and IS_VALID_PAE_ROOT
  KVM: X86/MMU: Don't use mmu->pae_root when shadowing PAE NPT in 64-bit
    host
  KVM: X86/MMU: Remove mmu_alloc_special_roots()

 arch/x86/include/asm/kvm_host.h |   5 +-
 arch/x86/kvm/mmu/mmu.c          | 575 ++++++++++++++------------------
 arch/x86/kvm/mmu/mmu_internal.h |  10 -
 arch/x86/kvm/mmu/paging_tmpl.h  |  51 ++-
 arch/x86/kvm/mmu/spte.c         |   7 +
 arch/x86/kvm/mmu/spte.h         |   1 +
 arch/x86/kvm/mmu/tdp_mmu.h      |   7 +-
 arch/x86/kvm/x86.c              |   4 +-
 8 files changed, 303 insertions(+), 357 deletions(-)

-- 
2.19.1.6.gb485710b