Re: [PATCH v4 1/5] KVM: MMU: fix release noslot pfn

Marcelo Tosatti
2012-10-10T15:12:23Z

On Sun, Oct 07, 2012 at 08:01:34PM +0800, Xiao Guangrong wrote:
> We can not directly call kvm_release_pfn_clean to release the pfn
> since we can meet noslot pfn which is used to cache mmio info into
> spte
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
> ---
> arch/x86/kvm/mmu.c | 3 +--
> virt/kvm/kvm_main.c | 4 +---
> 2 files changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index d289fee..6f85fe0 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2497,8 +2497,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> }
> }
>
> - if (!is_error_pfn(pfn))
> - kvm_release_pfn_clean(pfn);
> + kvm_release_pfn_clean(pfn);
> }
>
> static void nonpaging_new_cr3(struct kvm_vcpu *vcpu)
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index cc3f6dc..b65ec97 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1322,9 +1322,7 @@ EXPORT_SYMBOL_GPL(kvm_release_page_clean);
>
> void kvm_release_pfn_clean(pfn_t pfn)
> {
> - WARN_ON(is_error_pfn(pfn));
> -
> - if (!kvm_is_mmio_pfn(pfn))
> + if (!is_error_pfn(pfn) && !kvm_is_mmio_pfn(pfn))
> put_page(pfn_to_page(pfn));
> }
> EXPORT_SYMBOL_GPL(kvm_release_pfn_clean);
> --
> 1.7.7.6

Why does is_error_pfn() return true for mmio spte? Its not an "error",
after all.

Please kill is_invalid_pfn and use

-> is_error_pfn for checking for errors (mmio spte is not an error pfn,
its a special pfn)

-> add explicit is_noslot_pfn checks where necessary in the code
(say to avoid interpreting a noslot_pfn's pfn "address" bits).

(should have noticed this earlier, sorry).