Re: [PATCH v3 3/4] KVM: PPC: Book3S HV: migrate remaining normal-GFNs to secure-GFNs in H_SVM_INIT_DONE

[Bharata B Rao <bharata@linux.ibm.com>]

On Fri, Jun 19, 2020 at 03:43:41PM -0700, Ram Pai wrote:
> H_SVM_INIT_DONE incorrectly assumes that the Ultravisor has explicitly

As noted in the last iteration, can you reword the above please?
I don't see it as an incorrect assumption, but see it as extension of
scope now :-)

> called H_SVM_PAGE_IN for all secure pages. These GFNs continue to be
> normal GFNs associated with normal PFNs; when infact, these GFNs should
> have been secure GFNs, associated with device PFNs.
> 
> Move all the PFNs associated with the SVM's GFNs, to secure-PFNs, in
> H_SVM_INIT_DONE. Skip the GFNs that are already Paged-in or Shared
> through H_SVM_PAGE_IN, or Paged-in followed by a Paged-out through
> UV_PAGE_OUT.
> 
> Cc: Paul Mackerras <paulus@ozlabs.org>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Bharata B Rao <bharata@linux.ibm.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
> Cc: Laurent Dufour <ldufour@linux.ibm.com>
> Cc: Thiago Jung Bauermann <bauerman@linux.ibm.com>
> Cc: David Gibson <david@gibson.dropbear.id.au>
> Cc: Claudio Carvalho <cclaudio@linux.ibm.com>
> Cc: kvm-ppc@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> ---
>  Documentation/powerpc/ultravisor.rst        |   2 +
>  arch/powerpc/include/asm/kvm_book3s_uvmem.h |   2 +
>  arch/powerpc/kvm/book3s_hv_uvmem.c          | 154 +++++++++++++++++++++++-----
>  3 files changed, 132 insertions(+), 26 deletions(-)
> 
> diff --git a/Documentation/powerpc/ultravisor.rst b/Documentation/powerpc/ultravisor.rst
> index 363736d..3bc8957 100644
> --- a/Documentation/powerpc/ultravisor.rst
> +++ b/Documentation/powerpc/ultravisor.rst
> @@ -933,6 +933,8 @@ Return values
>  	* H_UNSUPPORTED		if called from the wrong context (e.g.
>  				from an SVM or before an H_SVM_INIT_START
>  				hypercall).
> +	* H_STATE		if the hypervisor could not successfully
> +                                transition the VM to Secure VM.
>  
>  Description
>  ~~~~~~~~~~~
> diff --git a/arch/powerpc/include/asm/kvm_book3s_uvmem.h b/arch/powerpc/include/asm/kvm_book3s_uvmem.h
> index 5a9834e..b9cd7eb 100644
> --- a/arch/powerpc/include/asm/kvm_book3s_uvmem.h
> +++ b/arch/powerpc/include/asm/kvm_book3s_uvmem.h
> @@ -22,6 +22,8 @@ unsigned long kvmppc_h_svm_page_out(struct kvm *kvm,
>  unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm);
>  void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
>  			     struct kvm *kvm, bool skip_page_out);
> +int kvmppc_uv_migrate_mem_slot(struct kvm *kvm,
> +			const struct kvm_memory_slot *memslot);
>  #else
>  static inline int kvmppc_uvmem_init(void)
>  {
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index c8c0290..449e8a7 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -93,6 +93,7 @@
>  #include <asm/ultravisor.h>
>  #include <asm/mman.h>
>  #include <asm/kvm_ppc.h>
> +#include <asm/kvm_book3s_uvmem.h>
>  
>  static struct dev_pagemap kvmppc_uvmem_pgmap;
>  static unsigned long *kvmppc_uvmem_bitmap;
> @@ -339,6 +340,21 @@ static bool kvmppc_gfn_is_uvmem_pfn(unsigned long gfn, struct kvm *kvm,
>  	return false;
>  }
>  
> +/* return true, if the GFN is a shared-GFN, or a secure-GFN */
> +bool kvmppc_gfn_has_transitioned(unsigned long gfn, struct kvm *kvm)
> +{
> +	struct kvmppc_uvmem_slot *p;
> +
> +	list_for_each_entry(p, &kvm->arch.uvmem_pfns, list) {
> +		if (gfn >= p->base_pfn && gfn < p->base_pfn + p->nr_pfns) {
> +			unsigned long index = gfn - p->base_pfn;
> +
> +			return (p->pfns[index] & KVMPPC_GFN_FLAG_MASK);
> +		}
> +	}
> +	return false;
> +}
> +
>  unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
>  {
>  	struct kvm_memslots *slots;
> @@ -379,12 +395,31 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
>  
>  unsigned long kvmppc_h_svm_init_done(struct kvm *kvm)
>  {
> +	struct kvm_memslots *slots;
> +	struct kvm_memory_slot *memslot;
> +	int srcu_idx;
> +	long ret = H_SUCCESS;
> +
>  	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
>  		return H_UNSUPPORTED;
>  
> +	/* migrate any unmoved normal pfn to device pfns*/
> +	srcu_idx = srcu_read_lock(&kvm->srcu);
> +	slots = kvm_memslots(kvm);
> +	kvm_for_each_memslot(memslot, slots) {
> +		ret = kvmppc_uv_migrate_mem_slot(kvm, memslot);
> +		if (ret) {
> +			ret = H_STATE;
> +			goto out;
> +		}
> +	}
> +
>  	kvm->arch.secure_guest |= KVMPPC_SECURE_INIT_DONE;
>  	pr_info("LPID %d went secure\n", kvm->arch.lpid);
> -	return H_SUCCESS;
> +
> +out:
> +	srcu_read_unlock(&kvm->srcu, srcu_idx);
> +	return ret;
>  }
>  
>  /*
> @@ -505,12 +540,14 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm)
>  }
>  
>  /*
> - * Alloc a PFN from private device memory pool and copy page from normal
> - * memory to secure memory using UV_PAGE_IN uvcall.
> + * Alloc a PFN from private device memory pool. If @pagein is true,
> + * copy page from normal memory to secure memory using UV_PAGE_IN uvcall.
>   */
> -static int kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
> -		   unsigned long end, unsigned long gpa, struct kvm *kvm,
> -		   unsigned long page_shift, bool *downgrade)
> +static int kvmppc_svm_migrate_page(struct vm_area_struct *vma,
> +		unsigned long start,
> +		unsigned long end, unsigned long gpa, struct kvm *kvm,
> +		unsigned long page_shift,
> +		bool pagein)
>  {
>  	unsigned long src_pfn, dst_pfn = 0;
>  	struct migrate_vma mig;
> @@ -526,18 +563,6 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
>  	mig.src = &src_pfn;
>  	mig.dst = &dst_pfn;
>  
> -	/*
> -	 * We come here with mmap_sem write lock held just for
> -	 * ksm_madvise(), otherwise we only need read mmap_sem.
> -	 * Hence downgrade to read lock once ksm_madvise() is done.
> -	 */

Can you please retain this comment? This explains why we take write lock
and then downgrade.

> -	ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> -			  MADV_UNMERGEABLE, &vma->vm_flags);
> -	downgrade_write(&kvm->mm->mmap_sem);
> -	*downgrade = true;

When I introduced this variable, there was a suggestion to rename it
to "downgraded", but we were a bit late then. When you are touching
this now, can you rename it appropriately?

> -	if (ret)
> -		return ret;
> -
>  	ret = migrate_vma_setup(&mig);
>  	if (ret)
>  		return ret;
> @@ -553,11 +578,16 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
>  		goto out_finalize;
>  	}
>  
> -	pfn = *mig.src >> MIGRATE_PFN_SHIFT;
> -	spage = migrate_pfn_to_page(*mig.src);
> -	if (spage)
> -		uv_page_in(kvm->arch.lpid, pfn << page_shift, gpa, 0,
> -			   page_shift);
> +	if (pagein) {
> +		pfn = *mig.src >> MIGRATE_PFN_SHIFT;
> +		spage = migrate_pfn_to_page(*mig.src);
> +		if (spage) {
> +			ret = uv_page_in(kvm->arch.lpid, pfn << page_shift,
> +					gpa, 0, page_shift);
> +			if (ret)
> +				goto out_finalize;
> +		}
> +	}
>  
>  	*mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
>  	migrate_vma_pages(&mig);
> @@ -566,6 +596,66 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
>  	return ret;
>  }
>  
> +int kvmppc_uv_migrate_mem_slot(struct kvm *kvm,
> +		const struct kvm_memory_slot *memslot)
> +{
> +	unsigned long gfn = memslot->base_gfn;
> +	unsigned long end;
> +	bool downgrade = false;
> +	struct vm_area_struct *vma;
> +	int i, ret = 0;
> +	unsigned long start = gfn_to_hva(kvm, gfn);
> +
> +	if (kvm_is_error_hva(start))
> +		return H_STATE;
> +
> +	end = start + (memslot->npages << PAGE_SHIFT);
> +
> +	down_write(&kvm->mm->mmap_sem);
> +
> +	mutex_lock(&kvm->arch.uvmem_lock);
> +	vma = find_vma_intersection(kvm->mm, start, end);
> +	if (!vma || vma->vm_start > start || vma->vm_end < end) {
> +		ret = H_STATE;
> +		goto out_unlock;
> +	}
> +
> +	ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> +			  MADV_UNMERGEABLE, &vma->vm_flags);
> +	downgrade_write(&kvm->mm->mmap_sem);
> +	downgrade = true;
> +	if (ret) {
> +		ret = H_STATE;
> +		goto out_unlock;
> +	}
> +
> +	for (i = 0; i < memslot->npages; i++, ++gfn) {
> +		/*
> +		 * skip GFNs that have already tranistioned.
> +		 * paged-in GFNs, shared GFNs, paged-in GFNs
> +		 * that were later paged-out.
> +		 */
> +		if (kvmppc_gfn_has_transitioned(gfn, kvm))
> +			continue;
> +
> +		start = gfn_to_hva(kvm, gfn);
> +		end = start + (1UL << PAGE_SHIFT);
> +		ret = kvmppc_svm_migrate_page(vma, start, end,
> +			(gfn << PAGE_SHIFT), kvm, PAGE_SHIFT, false);
> +

As I said last time, you are assuming that the vma that you obtained
in the beginning actually spans the entire memslot range. This might
be true as you haven't found any issues during testing, but I feel it
is better if there is no such implicit assumption in the code here.

Regards,
Bharata.