leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

KVM: x86/mmu: Drop RCU after processing each root in MMU notifier hooks

Browse Source 
Drop RCU protection after processing each root when handling MMU notifier
hooks that aren't the "unmap" path, i.e. aren't zapping.  Temporarily
drop RCU to let RCU do its thing between roots, and to make it clear that
there's no special behavior that relies on holding RCU across all roots.

Currently, the RCU protection is completely superficial, it's necessary
only to make rcu_dereference() of SPTE pointers happy.  A future patch
will rely on holding RCU as a proxy for vCPUs in the guest, e.g. to
ensure shadow pages aren't freed before all vCPUs do a TLB flush (or
rather, acknowledge the need for a flush), but in that case RCU needs to
be held until the flush is complete if and only if the flush is needed
because a shadow page may have been removed.  And except for the "unmap"
path, MMU notifier events cannot remove SPs (don't toggle PRESENT bit,
and can't change the PFN for a SP).

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220226001546.360188-10-seanjc@google.com>
Reviewed-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-02-26 00:15:27 +00:00 committed by Paolo Bonzini
parent 93fa50f644
commit a151aceca1
1 changed files with 4 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
arch/x86/kvm/mmu/tdp_mmu.c
View File

@ -1123,18 +1123,18 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
struct tdp_iter iter;
bool ret = false;
rcu_read_lock();
/*
* Don't support rescheduling, none of the MMU notifiers that funnel
* into this helper allow blocking; it'd be dead, wasteful code.
*/
for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
rcu_read_lock();
tdp_root_for_each_leaf_pte(iter, root, range->start, range->end)
ret |= handler(kvm, &iter, range);
}
rcu_read_unlock();
rcu_read_unlock();
}
return ret;
}