Marcelo Tosatti wrote:
> On Wed, Feb 13, 2008 at 08:45:51AM +0200, Avi Kivity wrote:
>
>>> gfn_to_page() needs to grab the struct page corresponding to the large
>>> page, not the offset struct page for the faulting 4k address within
>>> the large frame. Since gfn_to_page can sleep, there is no way to do
>>> that in the mapping logic which happens under mmu_lock protection.
>>> We don't want to grab the large page frame "struct page" unless the
>>> is_largepage_backed() checks are successful.
>>>
>>> The checks could be done in page_fault() if walker->level == 2, before
>>> gfn_to_page()... But I don't see much difference of that and doing
>>> it inside walk_addr(). What do you say?
>>>
>>>
>>>
>> I'd like to keep walk_addr() independent of the rest of the mmu (i.e.
>> walk_addr is 100% guest oriented). Also, the issue you point out is
>> shared by direct_map which doesn't call walk_addr().
>>
>> An unrelated issue (pointed out by Jun Nakajima) is that this kills
>> dirty log tracking (needed for migration). It could be solved simply by
>> not using large page backing if dirty log tracking is enabled for that slot.
>>
>
> Ok, fixed your comments and a bug which a root page was shadowed in the
> large area being mapped. access.flat is happy.
>
> Joerg, can you give this a try on a NPT-enabled system (need the
> attached qemu-largepage-hack.patch).
>
> Thanks
>
> Index: kvm.largepages/arch/x86/kvm/mmu.c
> ===================================================================
> --- kvm.largepages.orig/arch/x86/kvm/mmu.c
> +++ kvm.largepages/arch/x86/kvm/mmu.c
> @@ -27,6 +27,7 @@
> #include <linux/highmem.h>
> #include <linux/module.h>
> #include <linux/swap.h>
> +#include <linux/hugetlb.h>
>
> #include <asm/page.h>
> #include <asm/cmpxchg.h>
> @@ -211,6 +212,11 @@ static int is_shadow_present_pte(u64 pte
> && pte != shadow_notrap_nonpresent_pte;
> }
>
> +static int is_large_pte(u64 pte)
> +{
> + return pte & PT_PAGE_SIZE_MASK;
> +}
> +
> static int is_writeble_pte(unsigned long pte)
> {
> return pte & PT_WRITABLE_MASK;
> @@ -350,17 +356,120 @@ static void mmu_free_rmap_desc(struct kv
> kfree(rd);
> }
>
> +static int hpage_align_diff(unsigned long gfn)
> +{
> + return ((gfn+KVM_PAGES_PER_HPAGE-1) & ~(KVM_PAGES_PER_HPAGE-1)) - gfn;
> +}
> +
> +/*
> + * Return the pointer to the largepage write count for a given
> + * gfn, handling slots that are not large page aligned.
> + */
> +static int *slot_largepage_idx(gfn_t gfn, struct kvm_memory_slot *slot)
> +{
> + unsigned long idx;
> +
> + idx = (gfn - slot->base_gfn) + hpage_align_diff(slot->base_gfn);
> + idx /= KVM_PAGES_PER_HPAGE;
> + return &slot->lpage_info[idx].write_count;
> +}
>
Can be further simplified to (gfn / KVM_PAGES_PER_HPAGE) -
(slot->base_gfn / KVM_PAGES_PER_HPAGE). Sorry for not noticing earlier.
> +
> +static int is_largepage_backed(struct kvm_vcpu *vcpu, gfn_t large_gfn)
> +{
> + struct kvm_memory_slot *slot;
> +
> + if (has_wrprotected_page(vcpu->kvm, large_gfn))
> + return 0;
> +
> + if (!host_largepage_backed(vcpu->kvm, large_gfn))
> + return 0;
> +
> + slot = gfn_to_memslot(vcpu->kvm, large_gfn);
> + if (slot && slot->dirty_bitmap)
> + return 0;
> +
> + /* guest has 4M pages, host 2M */
> + if (!is_pae(vcpu) && HPAGE_SHIFT == 21)
> + return 0;
>
Is this check necessary? I think that if we remove it things will just
work. A 4MB page will be have either one or two 2MB sptes (which may
even belong to different slots).
> @@ -894,12 +1030,28 @@ struct page *gva_to_page(struct kvm_vcpu
> static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
> unsigned pt_access, unsigned pte_access,
> int user_fault, int write_fault, int dirty,
> - int *ptwrite, gfn_t gfn, struct page *page)
> + int *ptwrite, int largepage, gfn_t gfn,
> + struct page *page)
> {
> u64 spte;
> int was_rmapped = is_rmap_pte(*shadow_pte);
> int was_writeble = is_writeble_pte(*shadow_pte);
>
> + /*
> + * If we overwrite a PTE page pointer with a 2MB PMD, unlink
> + * the parent of the now unreachable PTE.
> + */
> + if (largepage) {
> + if (was_rmapped && !is_large_pte(*shadow_pte)) {
> + struct kvm_mmu_page *child;
> + u64 pte = *shadow_pte;
> +
> + child = page_header(pte & PT64_BASE_ADDR_MASK);
> + mmu_page_remove_parent_pte(child, shadow_pte);
> + }
> + was_rmapped = is_large_pte(*shadow_pte);
> + }
> +
> pgprintk("%s: spte %llx access %x write_fault %d"
> " user_fault %d gfn %lx\n",
> __FUNCTION__, *shadow_pte, pt_access,
> @@ -919,6 +1071,8 @@ static void mmu_set_spte(struct kvm_vcpu
> spte |= PT_PRESENT_MASK;
> if (pte_access & ACC_USER_MASK)
> spte |= PT_USER_MASK;
> + if (largepage)
> + spte |= PT_PAGE_SIZE_MASK;
>
> spte |= page_to_phys(page);
>
> @@ -933,7 +1087,8 @@ static void mmu_set_spte(struct kvm_vcpu
> }
>
> shadow = kvm_mmu_lookup_page(vcpu->kvm, gfn);
> - if (shadow) {
> + if (shadow ||
> + (largepage && has_wrprotected_page(vcpu->kvm, gfn))) {
> pgprintk("%s: found shadow page for %lx, marking ro\n",
> __FUNCTION__, gfn);
> pte_access &= ~ACC_WRITE_MASK;
> @@ -941,6 +1096,18 @@ static void mmu_set_spte(struct kvm_vcpu
> spte &= ~PT_WRITABLE_MASK;
> kvm_x86_ops->tlb_flush(vcpu);
> }
> + /*
> + * Largepage creation is susceptible to a upper-level
> + * table to be shadowed and write-protected in the
> + * area being mapped. If that is the case, invalidate
> + * the entry and let the instruction fault again
> + * and use 4K mappings.
> + */
> + if (largepage) {
> + spte = shadow_trap_nonpresent_pte;
> + kvm_x86_ops->tlb_flush(vcpu);
> + goto unshadowed;
> + }
>
Would it not repeat exactly the same code path? Or is this just for the
case of the pte_update path?
> - page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
> + if (is_largepage_backed(vcpu, gfn & ~(KVM_PAGES_PER_HPAGE-1))
> + && is_physical_memory(vcpu->kvm, gfn)) {
> + gfn &= ~(KVM_PAGES_PER_HPAGE-1);
> + largepage = 1;
> + }
>
Doesn't is_largepage_backed() imply is_physical_memory?
>
> Index: kvm.largepages/arch/x86/kvm/x86.c
> ===================================================================
> --- kvm.largepages.orig/arch/x86/kvm/x86.c
> +++ kvm.largepages/arch/x86/kvm/x86.c
> @@ -86,6 +86,7 @@ struct kvm_stats_debugfs_item debugfs_en
> { "mmu_recycled", VM_STAT(mmu_recycled) },
> { "mmu_cache_miss", VM_STAT(mmu_cache_miss) },
> { "remote_tlb_flush", VM_STAT(remote_tlb_flush) },
> + { "lpages", VM_STAT(lpages) },
> { NULL }
> };
>
s/lpages/largepages/, this is user visible.
> + new.lpage_info = vmalloc(largepages * sizeof(*new.lpage_info));
> +
> + if (!new.lpage_info)
> + goto out_free;
> +
> + memset(new.lpage_info, 0, largepages * sizeof(*new.lpage_info));
> + /* large page crosses memslot boundary */
> + if (npages % KVM_PAGES_PER_HPAGE) {
> + new.lpage_info[0].write_count = 1;
>
This seems wrong, say a 3MB slot at 1GB, you kill the first largepage
which is good.
> + new.lpage_info[largepages-1].write_count = 1;
>
OTOH, a 3MB slot at 3MB, the last page is fine. The check needs to be
against base_gfn and base_gfn + npages, not the number of pages.
> + }
>
> + }
>
> /* Allocate page dirty bitmap if needed */
> if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) {
> @@ -444,7 +464,7 @@ int kvm_is_visible_gfn(struct kvm *kvm,
> }
> EXPORT_SYMBOL_GPL(kvm_is_visible_gfn);
>
> -static unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
> +unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
> {
> struct kvm_memory_slot *slot;
>
> @@ -454,6 +474,7 @@ static unsigned long gfn_to_hva(struct k
> return bad_hva();
> return (slot->userspace_addr + (gfn - slot->base_gfn) * PAGE_SIZE);
> }
> +EXPORT_SYMBOL(gfn_to_hva);
>
> /*
> * Requires current->mm->mmap_sem to be held
>
> ------------------------------------------------------------------------
>
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