Hi Will,
On 8/18/20 11:27 PM, Will Deacon wrote:
kvm_phys_addr_ioremap() unconditionally empties out the memcache pages
for the current vCPU on return. This causes subsequent topups to allocate
fresh pages and is at odds with the behaviour when mapping memory in
user_mem_abort().
Remove the call to kvm_mmu_free_memory_cache() from
kvm_phys_addr_ioremap(), allowing the cached pages to be used by a later
mapping.
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Quentin Perret <qperret@xxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
arch/arm64/kvm/mmu.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 662b0c99a63d..4a24ebdc6fc6 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1489,19 +1489,17 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
ret = kvm_mmu_topup_memory_cache(&cache,
kvm_mmu_cache_min_pages(kvm));
if (ret)
- goto out;
+ break;
spin_lock(&kvm->mmu_lock);
ret = stage2_set_pte(&kvm->arch.mmu, &cache, addr, &pte,
KVM_S2PTE_FLAG_IS_IOMAP);
spin_unlock(&kvm->mmu_lock);
if (ret)
- goto out;
+ break;
pfn++;
}
-out:
- kvm_mmu_free_memory_cache(&cache);
return ret;
}
It seems incorrect. The cache is tracked by local variable (@cache),
meaning the cache is only visible to kvm_phys_addr_ioremap() and its
callee. So it's correct to free unused pages in two cases: (1) error
is returned (2) high level of page tables were previously populated
and not all pre-allocated pages are used. Otherwise, this leads to
memory leakage.
Thanks,
Gavin
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