Re: [RFCv2 15/16] KVM: Unmap protected pages from direct mapping

[Mike Rapoport]

On Tue, Oct 20, 2020 at 09:18:58AM +0300, Kirill A. Shutemov wrote:
> If the protected memory feature enabled, unmap guest memory from
> kernel's direct mappings.
> 
> Migration and KSM is disabled for protected memory as it would require a
> special treatment.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
>  include/linux/mm.h       |  3 +++
>  mm/huge_memory.c         |  8 ++++++++
>  mm/ksm.c                 |  2 ++
>  mm/memory.c              | 12 ++++++++++++
>  mm/rmap.c                |  4 ++++
>  virt/lib/mem_protected.c | 21 +++++++++++++++++++++
>  6 files changed, 50 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ee274d27e764..74efc51e63f0 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -671,6 +671,9 @@ static inline bool vma_is_kvm_protected(struct vm_area_struct *vma)
>  	return vma->vm_flags & VM_KVM_PROTECTED;
>  }
>  
> +void kvm_map_page(struct page *page, int nr_pages);
> +void kvm_unmap_page(struct page *page, int nr_pages);

This still does not seem right ;-)

And I still think that map/unmap primitives shoud be a part of the
generic mm rather than exported by KVM.

> +
>  #ifdef CONFIG_SHMEM
>  /*
>   * The vma_is_shmem is not inline because it is used only by slow
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index ec8cf9a40cfd..40974656cb43 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -627,6 +627,10 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
>  		spin_unlock(vmf->ptl);
>  		count_vm_event(THP_FAULT_ALLOC);
>  		count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
> +
> +		/* Unmap page from direct mapping */
> +		if (vma_is_kvm_protected(vma))
> +			kvm_unmap_page(page, HPAGE_PMD_NR);
>  	}
>  
>  	return 0;
> @@ -1689,6 +1693,10 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>  			page_remove_rmap(page, true);
>  			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
>  			VM_BUG_ON_PAGE(!PageHead(page), page);
> +
> +			/* Map the page back to the direct mapping */
> +			if (vma_is_kvm_protected(vma))
> +				kvm_map_page(page, HPAGE_PMD_NR);
>  		} else if (thp_migration_supported()) {
>  			swp_entry_t entry;
>  
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 9afccc36dbd2..c720e271448f 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -528,6 +528,8 @@ static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
>  		return NULL;
>  	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
>  		return NULL;
> +	if (vma_is_kvm_protected(vma))
> +		return NULL;
>  	return vma;
>  }
>  
> diff --git a/mm/memory.c b/mm/memory.c
> index 2c9756b4e52f..e28bd5f902a7 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1245,6 +1245,11 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  				    likely(!(vma->vm_flags & VM_SEQ_READ)))
>  					mark_page_accessed(page);
>  			}
> +
> +			/* Map the page back to the direct mapping */
> +			if (vma_is_anonymous(vma) && vma_is_kvm_protected(vma))
> +				kvm_map_page(page, 1);
> +
>  			rss[mm_counter(page)]--;
>  			page_remove_rmap(page, false);
>  			if (unlikely(page_mapcount(page) < 0))
> @@ -3466,6 +3471,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>  	struct page *page;
>  	vm_fault_t ret = 0;
>  	pte_t entry;
> +	bool set = false;
>  
>  	/* File mapping without ->vm_ops ? */
>  	if (vma->vm_flags & VM_SHARED)
> @@ -3554,6 +3560,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>  	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
>  	page_add_new_anon_rmap(page, vma, vmf->address, false);
>  	lru_cache_add_inactive_or_unevictable(page, vma);
> +	set = true;
>  setpte:
>  	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);
>  
> @@ -3561,6 +3568,11 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>  	update_mmu_cache(vma, vmf->address, vmf->pte);
>  unlock:
>  	pte_unmap_unlock(vmf->pte, vmf->ptl);
> +
> +	/* Unmap page from direct mapping */
> +	if (vma_is_kvm_protected(vma) && set)
> +		kvm_unmap_page(page, 1);
> +
>  	return ret;
>  release:
>  	put_page(page);
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 9425260774a1..247548d6d24b 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1725,6 +1725,10 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  
>  static bool invalid_migration_vma(struct vm_area_struct *vma, void *arg)
>  {
> +	/* TODO */
> +	if (vma_is_kvm_protected(vma))
> +		return true;
> +
>  	return vma_is_temporary_stack(vma);
>  }
>  
> diff --git a/virt/lib/mem_protected.c b/virt/lib/mem_protected.c
> index 1dfe82534242..9d2ef99285e5 100644
> --- a/virt/lib/mem_protected.c
> +++ b/virt/lib/mem_protected.c
> @@ -30,6 +30,27 @@ void kvm_unmap_page_atomic(void *vaddr)
>  }
>  EXPORT_SYMBOL_GPL(kvm_unmap_page_atomic);
>  
> +void kvm_map_page(struct page *page, int nr_pages)
> +{
> +	int i;
> +
> +	/* Clear page before returning it to the direct mapping */
> +	for (i = 0; i < nr_pages; i++) {
> +		void *p = kvm_map_page_atomic(page + i);
> +		memset(p, 0, PAGE_SIZE);
> +		kvm_unmap_page_atomic(p);
> +	}
> +
> +	kernel_map_pages(page, nr_pages, 1);
> +}
> +EXPORT_SYMBOL_GPL(kvm_map_page);
> +
> +void kvm_unmap_page(struct page *page, int nr_pages)
> +{
> +	kernel_map_pages(page, nr_pages, 0);
> +}
> +EXPORT_SYMBOL_GPL(kvm_unmap_page);
> +
>  int kvm_init_protected_memory(void)
>  {
>  	guest_map_ptes = kmalloc_array(num_possible_cpus(),
> -- 
> 2.26.2
> 
> 

-- 
Sincerely yours,
Mike.