On Mon, Mar 30, 2020 at 09:32:40PM +0800, Zhuang Yanying wrote:
From: LinFeng linfeng23@huawei.com
We found that the !is_zero_page() in kvm_is_mmio_pfn() was submmited in commit:90cff5a8cc("KVM: check for !is_zero_pfn() in kvm_is_mmio_pfn()"), but reverted in commit:0ef2459983("kvm: fix kvm_is_mmio_pfn() and rename to kvm_is_reserved_pfn()").
Maybe just adding !is_zero_page() to kvm_is_reserved_pfn() is too rough. According to commit:e433e83bc3("KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved"), special handling in some other flows is also need by zero_page, if we treat zero_page as being reserved.
Well, as fixing all functions reference to kvm_is_reserved_pfn() in this patch, we found that only kvm_release_pfn_clean() and kvm_get_pfn() don't need special handling.
So, we thought why not only check is_zero_page() in before get and put page, and revert our last commit:31e813f38f("KVM: fix overflow of zero page refcount with ksm running"). Instead of add !is_zero_page() in kvm_is_reserved_pfn(), new idea is as follow:
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7f9ee2929cfe..f9a1f9cf188e 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1695,7 +1695,8 @@ EXPORT_SYMBOL_GPL(kvm_release_page_clean); void kvm_release_pfn_clean(kvm_pfn_t pfn) {
- if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn))
- if (!is_error_noslot_pfn(pfn) &&
(!kvm_is_reserved_pfn(pfn) || is_zero_pfn(pfn)))} EXPORT_SYMBOL_GPL(kvm_release_pfn_clean); @@ -1734,7 +1735,7 @@ EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed); void kvm_get_pfn(kvm_pfn_t pfn) {
- if (!kvm_is_reserved_pfn(pfn))
- if (!kvm_is_reserved_pfn(pfn) || is_zero_pfn(pfn)) get_page(pfn_to_page(pfn));
} EXPORT_SYMBOL_GPL(kvm_get_pfn);
We are confused why ZONE_DEVICE not do this, but treating it as no reserved. Is it racy if we change only use the patch in cover letter, but not the series patches.
LinFeng (1): KVM: special handling of zero_page in some flows
Zhuang Yanying (1): KVM: fix overflow of zero page refcount with ksm running
arch/x86/kvm/mmu.c | 2 ++ virt/kvm/kvm_main.c | 9 +++++---- 2 files changed, 7 insertions(+), 4 deletions(-)
-- 2.23.0
<formletter>
This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly.
</formletter>