Re: [PATCH 2/2] kvm: fix kvm_is_mmio_pfn() and rename to kvm_is_reserved_pfn()

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/11/2014 09:33, Ard Biesheuvel wrote:
> This reverts commit 85c8555ff0 ("KVM: check for !is_zero_pfn() in
> kvm_is_mmio_pfn()") and renames the function to kvm_is_reserved_pfn.
> 
> The problem being addressed by the patch above was that some ARM code
> based the memory mapping attributes of a pfn on the return value of
> kvm_is_mmio_pfn(), whose name indeed suggests that such pfns should
> be mapped as device memory.
> 
> However, kvm_is_mmio_pfn() doesn't do quite what it says on the tin,
> and the existing non-ARM users were already using it in a way which
> suggests that its name should probably have been 'kvm_is_reserved_pfn'
> from the beginning, e.g., whether or not to call get_page/put_page on
> it etc. This means that returning false for the zero page is a mistake
> and the patch above should be reverted.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  arch/ia64/kvm/kvm-ia64.c |  2 +-
>  arch/x86/kvm/mmu.c       |  6 +++---
>  include/linux/kvm_host.h |  2 +-
>  virt/kvm/kvm_main.c      | 16 ++++++++--------
>  4 files changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
> index ec6b9acb6bea..dbe46f43884d 100644
> --- a/arch/ia64/kvm/kvm-ia64.c
> +++ b/arch/ia64/kvm/kvm-ia64.c
> @@ -1563,7 +1563,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  
>  	for (i = 0; i < npages; i++) {
>  		pfn = gfn_to_pfn(kvm, base_gfn + i);
> -		if (!kvm_is_mmio_pfn(pfn)) {
> +		if (!kvm_is_reserved_pfn(pfn)) {
>  			kvm_set_pmt_entry(kvm, base_gfn + i,
>  					pfn << PAGE_SHIFT,
>  				_PAGE_AR_RWX | _PAGE_MA_WB);
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index ac1c4de3a484..978f402006ee 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -630,7 +630,7 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
>  	 * kvm mmu, before reclaiming the page, we should
>  	 * unmap it from mmu first.
>  	 */
> -	WARN_ON(!kvm_is_mmio_pfn(pfn) && !page_count(pfn_to_page(pfn)));
> +	WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn)));
>  
>  	if (!shadow_accessed_mask || old_spte & shadow_accessed_mask)
>  		kvm_set_pfn_accessed(pfn);
> @@ -2461,7 +2461,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>  		spte |= PT_PAGE_SIZE_MASK;
>  	if (tdp_enabled)
>  		spte |= kvm_x86_ops->get_mt_mask(vcpu, gfn,
> -			kvm_is_mmio_pfn(pfn));
> +			kvm_is_reserved_pfn(pfn));
>  
>  	if (host_writable)
>  		spte |= SPTE_HOST_WRITEABLE;
> @@ -2737,7 +2737,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
>  	 * PT_PAGE_TABLE_LEVEL and there would be no adjustment done
>  	 * here.
>  	 */
> -	if (!is_error_noslot_pfn(pfn) && !kvm_is_mmio_pfn(pfn) &&
> +	if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
>  	    level == PT_PAGE_TABLE_LEVEL &&
>  	    PageTransCompound(pfn_to_page(pfn)) &&
>  	    !has_wrprotected_page(vcpu->kvm, gfn, PT_DIRECTORY_LEVEL)) {
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index ea53b04993f2..a6059bdf7b03 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -703,7 +703,7 @@ void kvm_arch_sync_events(struct kvm *kvm);
>  int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu);
>  void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
>  
> -bool kvm_is_mmio_pfn(pfn_t pfn);
> +bool kvm_is_reserved_pfn(pfn_t pfn);
>  
>  struct kvm_irq_ack_notifier {
>  	struct hlist_node link;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 25ffac9e947d..3cee7b167052 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -107,10 +107,10 @@ EXPORT_SYMBOL_GPL(kvm_rebooting);
>  
>  static bool largepages_enabled = true;
>  
> -bool kvm_is_mmio_pfn(pfn_t pfn)
> +bool kvm_is_reserved_pfn(pfn_t pfn)
>  {
>  	if (pfn_valid(pfn))
> -		return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn));
> +		return PageReserved(pfn_to_page(pfn));
>  
>  	return true;
>  }
> @@ -1321,7 +1321,7 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
>  	else if ((vma->vm_flags & VM_PFNMAP)) {
>  		pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) +
>  			vma->vm_pgoff;
> -		BUG_ON(!kvm_is_mmio_pfn(pfn));
> +		BUG_ON(!kvm_is_reserved_pfn(pfn));
>  	} else {
>  		if (async && vma_is_valid(vma, write_fault))
>  			*async = true;
> @@ -1427,7 +1427,7 @@ static struct page *kvm_pfn_to_page(pfn_t pfn)
>  	if (is_error_noslot_pfn(pfn))
>  		return KVM_ERR_PTR_BAD_PAGE;
>  
> -	if (kvm_is_mmio_pfn(pfn)) {
> +	if (kvm_is_reserved_pfn(pfn)) {
>  		WARN_ON(1);
>  		return KVM_ERR_PTR_BAD_PAGE;
>  	}
> @@ -1456,7 +1456,7 @@ EXPORT_SYMBOL_GPL(kvm_release_page_clean);
>  
>  void kvm_release_pfn_clean(pfn_t pfn)
>  {
> -	if (!is_error_noslot_pfn(pfn) && !kvm_is_mmio_pfn(pfn))
> +	if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn))
>  		put_page(pfn_to_page(pfn));
>  }
>  EXPORT_SYMBOL_GPL(kvm_release_pfn_clean);
> @@ -1477,7 +1477,7 @@ static void kvm_release_pfn_dirty(pfn_t pfn)
>  
>  void kvm_set_pfn_dirty(pfn_t pfn)
>  {
> -	if (!kvm_is_mmio_pfn(pfn)) {
> +	if (!kvm_is_reserved_pfn(pfn)) {
>  		struct page *page = pfn_to_page(pfn);
>  		if (!PageReserved(page))
>  			SetPageDirty(page);
> @@ -1487,14 +1487,14 @@ EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
>  
>  void kvm_set_pfn_accessed(pfn_t pfn)
>  {
> -	if (!kvm_is_mmio_pfn(pfn))
> +	if (!kvm_is_reserved_pfn(pfn))
>  		mark_page_accessed(pfn_to_page(pfn));
>  }
>  EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);
>  
>  void kvm_get_pfn(pfn_t pfn)
>  {
> -	if (!kvm_is_mmio_pfn(pfn))
> +	if (!kvm_is_reserved_pfn(pfn))
>  		get_page(pfn_to_page(pfn));
>  }
>  EXPORT_SYMBOL_GPL(kvm_get_pfn);
> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Since this is in practice ARM only, I'll apply these for 3.18.

Paolo