On 10 November 2014 11:53, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote:
> Hi Ard,
>
> On Mon, Nov 10, 2014 at 09:33:56AM +0100, 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@xxxxxxxxxx>
>> ---
>> 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));
>
> so we return true for !pfn_valid(pfn), is this still semantically
> correct with the rename?
>
I guess it is still debatable, but is arguably more correct than
'kvm_is_mmio_pfn'
I was reluctant to choose something like 'kvm_is_special_pfn' because
'special' is not very discriminating here, and at least 'reserved' has
a very clear meaning wrt pages, and treating non-struct page backed
pfn's as reserved implicitly is not counter-intuitive imo.
>>
>> 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);
>
> this looks rather redundant now then? Or is it catering specifically to
> the situation where !pfn_valid(pfn) ?
>
I hadn't spotted this myself, to be honest, but that second test was
redundant to begin with, i.e., we never enter the block for a reserved
page.
I can remove it here, or in a followup patch, as you [plural] prefer.
>> @@ -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);
>> --
>> 1.8.3.2
>>
>
> Thanks for looking at this!
> -Christoffer
>
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