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KVM: x86/mmu: simplify kvm_tdp_mmu_map flow when guest has to retry

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A removed SPTE is never present, hence the "if" in kvm_tdp_mmu_map
only fails in the exact same conditions that the earlier loop
tested in order to issue a  "break". So, instead of checking twice the
condition (upper level SPTEs could not be created or was frozen), just
exit the loop with a goto---the usual poor-man C replacement for RAII
early returns.

While at it, do not use the "ret" variable for return values of
functions that do not return a RET_PF_* enum.  This is clearer
and also makes it possible to initialize ret to RET_PF_RETRY.

Suggested-by: Robert Hoo <robert.hu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2022-11-17 11:05:51 -05:00
parent c4b33d28ea
commit 63d28a25e0
1 changed files with 19 additions and 21 deletions
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40
arch/x86/kvm/mmu/tdp_mmu.c
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@ -1159,7 +1159,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
struct kvm *kvm = vcpu->kvm;
struct tdp_iter iter;
struct kvm_mmu_page *sp;
int ret;
int ret = RET_PF_RETRY;
kvm_mmu_hugepage_adjust(vcpu, fault);
@ -1168,23 +1168,25 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
rcu_read_lock();
tdp_mmu_for_each_pte(iter, mmu, fault->gfn, fault->gfn + 1) {
int r;
if (fault->nx_huge_page_workaround_enabled)
disallowed_hugepage_adjust(fault, iter.old_spte, iter.level);
if (iter.level == fault->goal_level)
break;
/* Step down into the lower level page table if it exists. */
if (is_shadow_present_pte(iter.old_spte) &&
!is_large_pte(iter.old_spte))
continue;
/*
* If SPTE has been frozen by another thread, just give up and
* retry, avoiding unnecessary page table allocation and free.
*/
if (is_removed_spte(iter.old_spte))
break;
goto retry;
/* Step down into the lower level page table if it exists. */
if (is_shadow_present_pte(iter.old_spte) &&
!is_large_pte(iter.old_spte))
continue;
/*
* The SPTE is either non-present or points to a huge page that
@ -1196,13 +1198,17 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
sp->nx_huge_page_disallowed = fault->huge_page_disallowed;
if (is_shadow_present_pte(iter.old_spte))
ret = tdp_mmu_split_huge_page(kvm, &iter, sp, true);
r = tdp_mmu_split_huge_page(kvm, &iter, sp, true);
else
ret = tdp_mmu_link_sp(kvm, &iter, sp, true);
r = tdp_mmu_link_sp(kvm, &iter, sp, true);
if (ret) {
/*
* Also force the guest to retry the access if the upper level SPTEs
* aren't in place.
*/
if (r) {
tdp_mmu_free_sp(sp);
break;
goto retry;
}
if (fault->huge_page_disallowed &&
@ -1213,18 +1219,10 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
}
}
/*
* Force the guest to retry the access if the upper level SPTEs aren't
* in place, or if the target leaf SPTE is frozen by another CPU.
*/
if (iter.level != fault->goal_level || is_removed_spte(iter.old_spte)) {
rcu_read_unlock();
return RET_PF_RETRY;
}
ret = tdp_mmu_map_handle_target_level(vcpu, fault, &iter);
rcu_read_unlock();
retry:
rcu_read_unlock();
return ret;
}