Third times a charm! Right? Right!?!?
Allocate the hashed list of shadow pages dynamically (separate from
struct kvm), and on-demand. The hashed list is 32KiB, i.e. absolutely
belongs in a separate allocation, and is worth skipping if KVM isn't
shadowing guest PTEs for the VM.
Side topic #1, a bunch of my measurements from v2 and ealier were "bad",
because I was using a PROVE_LOCKING=y kernel, which significantly inflates
the size of "struct kvm" in particular.
Side topic #2, I have a patch to dynamically allocate the memslots hash
tables (they're very conveniently either 2KiB or 4KiB in size for 64-bit
kernels), but I couldn't convince myself that the complexity is in any way
justified. I did however account for the size of the hash tables in the
assertions, if only to document where a big chunk of the per-VM memory usage
is going.
Side topic #3, AFAIK, DEBUG_KERNEL=n builds are quite rare, so I'm banking
on build bots tripping the assert (I'll also add a DEBUG_KERNEL=n config to
my own testing, probably).
v3:
- Add comments explaining the {READ,WRITE}_ONCE logic, and why it's safe
to set the list outside of mmu_lock. [Vipin]
- Make the assertions actually work. [Vipin]
- Refine the assertions so they (hopefully) won't fail on kernels with
a bunch of debug crud added.
v2:
- https://lore.kernel.org/all/20250401155714.838398-1-seanjc@xxxxxxxxxx
- Actually defer allocation when using TDP MMU. [Vipin]
- Free allocation on MMU teardown. [Vipin]
v1: https://lore.kernel.org/all/20250315024010.2360884-1-seanjc@xxxxxxxxxx
Sean Christopherson (3):
KVM: x86/mmu: Dynamically allocate shadow MMU's hashed page list
KVM: x86: Use kvzalloc() to allocate VM struct
KVM: x86/mmu: Defer allocation of shadow MMU's hashed page list
arch/x86/include/asm/kvm_host.h | 6 +--
arch/x86/kvm/mmu/mmu.c | 73 ++++++++++++++++++++++++++++++---
arch/x86/kvm/svm/svm.c | 2 +
arch/x86/kvm/vmx/main.c | 2 +
arch/x86/kvm/vmx/vmx.c | 2 +
arch/x86/kvm/x86.c | 5 ++-
arch/x86/kvm/x86.h | 22 ++++++++++
7 files changed, 102 insertions(+), 10 deletions(-)
base-commit: 7ef51a41466bc846ad794d505e2e34ff97157f7f
--
2.49.0.1112.g889b7c5bd8-goog
