On Tue, May 11, 2021, Sean Christopherson wrote: > On Tue, May 11, 2021, Ben Gardon wrote: > > If the TDP MMU is in use, wait to allocate the rmaps until the shadow > > MMU is actually used. (i.e. a nested VM is launched.) This saves memory > > equal to 0.2% of guest memory in cases where the TDP MMU is used and > > there are no nested guests involved. > > > > Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx> > > --- > > arch/x86/include/asm/kvm_host.h | 2 ++ > > arch/x86/kvm/mmu/mmu.c | 53 +++++++++++++++++++++++---------- > > arch/x86/kvm/mmu/tdp_mmu.c | 6 ++-- > > arch/x86/kvm/mmu/tdp_mmu.h | 4 +-- > > arch/x86/kvm/x86.c | 45 +++++++++++++++++++++++++++- > > 5 files changed, 89 insertions(+), 21 deletions(-) > > > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > > index fc75ed49bfee..7b65f82ade1c 100644 > > --- a/arch/x86/include/asm/kvm_host.h > > +++ b/arch/x86/include/asm/kvm_host.h > > @@ -1868,4 +1868,6 @@ static inline int kvm_cpu_get_apicid(int mps_cpu) > > > > int kvm_cpu_dirty_log_size(void); > > > > +int alloc_all_memslots_rmaps(struct kvm *kvm); > > + > > #endif /* _ASM_X86_KVM_HOST_H */ > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > index b0bdb924d519..183afccd2944 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -1190,7 +1190,8 @@ static void kvm_mmu_write_protect_pt_masked(struct kvm *kvm, > > kvm_tdp_mmu_clear_dirty_pt_masked(kvm, slot, > > slot->base_gfn + gfn_offset, mask, true); > > > > - if (!kvm->arch.memslots_have_rmaps) > > + /* Read memslots_have_rmaps before the rmaps themselves */ > > IIRC, you open coded reading memslots_have_rmaps because of a circular > dependency, but you can solve that simply by defining the helper in mmu.h > instead of kvm_host.h. > > And I think you could even make it static in mmu.c and omit the smp_load_acuquire > from the three users in x86.c, though that's probably not worth it. > > Either way, reading the same comment over and over and over, just to make > checkpatch happy, gets more than a bit tedious. > > That would also allow you to elaborate on why the smp_load_acquire() is > necessary, and preferably what it pairs with. Belated thought: you could also introduce the helper in patch 06 in order to miminize thrash in this patch.
