[PATCH V3 00/12] KVM: X86/MMU: Use one-off local shadow page for special roots

Lai Jiangshan
2022-05-21T13:16:14Z

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-jiangshanlai@gmail.com/
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-jiangshanlai@gmail.com/
[V1]: https://lore.kernel.org/lkml/20220420132605.3813-1-jiangshanlai@gmail.com/

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