Re: [PATCH RFC v7 11/64] KVM: SEV: Support private pages in LAUNCH_UPDATE_DATA

[erbse.13@gmx.de]

On Wed, Dec 14, 2022 at 01:40:03PM -0600, Michael Roth wrote:
> From: Nikunj A Dadhania <nikunj@amd.com>
>
> Pre-boot guest payload needs to be encrypted and VMM has copied it
> over to the private-fd. Add support to get the pfn from the memfile fd
> for encrypting the payload in-place.
>
> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---
>  arch/x86/kvm/svm/sev.c | 79 ++++++++++++++++++++++++++++++++++--------
>  1 file changed, 64 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a7e4e3005786..ae4920aeb281 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -107,6 +107,11 @@ static inline bool is_mirroring_enc_context(struct kvm *kvm)
>  	return !!to_kvm_svm(kvm)->sev_info.enc_context_owner;
>  }
>
> +static bool kvm_is_upm_enabled(struct kvm *kvm)
> +{
> +	return kvm->arch.upm_mode;
> +}
> +
>  /* Must be called with the sev_bitmap_lock held */
>  static bool __sev_recycle_asids(int min_asid, int max_asid)
>  {
> @@ -382,6 +387,38 @@ static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  	return ret;
>  }
>
> +static int sev_get_memfile_pfn_handler(struct kvm *kvm, struct kvm_gfn_range *range, void *data)
> +{
> +	struct kvm_memory_slot *memslot = range->slot;
> +	struct page **pages = data;
> +	int ret = 0, i = 0;
> +	kvm_pfn_t pfn;
> +	gfn_t gfn;
> +
> +	for (gfn = range->start; gfn < range->end; gfn++) {
> +		int order;
> +
> +		ret = kvm_restricted_mem_get_pfn(memslot, gfn, &pfn, &order);
> +		if (ret)
> +			return ret;
> +
> +		if (is_error_noslot_pfn(pfn))
> +			return -EFAULT;
> +
> +		pages[i++] = pfn_to_page(pfn);
> +	}
> +
> +	return ret;
> +}
> +
> +static int sev_get_memfile_pfn(struct kvm *kvm, unsigned long addr,
> +			       unsigned long size, unsigned long npages,
> +			       struct page **pages)
> +{
> +	return kvm_vm_do_hva_range_op(kvm, addr, size,
> +				      sev_get_memfile_pfn_handler, pages);
> +}

The third argument for the kvm_vm_do_hva_range_op call should be addr+size; the
function expects the end of the range not the size of the range.

> +
>  static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
>  				    unsigned long ulen, unsigned long *n,
>  				    int write)
> @@ -424,16 +461,25 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
>  	if (!pages)
>  		return ERR_PTR(-ENOMEM);
>
> -	/* Pin the user virtual address. */
> -	npinned = pin_user_pages_fast(uaddr, npages, write ? FOLL_WRITE : 0, pages);
> -	if (npinned != npages) {
> -		pr_err("SEV: Failure locking %lu pages.\n", npages);
> -		ret = -ENOMEM;
> -		goto err;
> +	if (kvm_is_upm_enabled(kvm)) {
> +		/* Get the PFN from memfile */
> +		if (sev_get_memfile_pfn(kvm, uaddr, ulen, npages, pages)) {
> +			pr_err("%s: ERROR: unable to find slot for uaddr %lx", __func__, uaddr);
> +			ret = -ENOMEM;
> +			goto err;
> +		}

This branch doesn't initialize npinned. If sev_get_memfile_pfn fails, the code following the err
label passes the uninitialized value to unpin_user_pages.

> +	} else {
> +		/* Pin the user virtual address. */
> +		npinned = pin_user_pages_fast(uaddr, npages, write ? FOLL_WRITE : 0, pages);
> +		if (npinned != npages) {
> +			pr_err("SEV: Failure locking %lu pages.\n", npages);
> +			ret = -ENOMEM;
> +			goto err;
> +		}
> +		sev->pages_locked = locked;
>  	}
>
>  	*n = npages;
> -	sev->pages_locked = locked;
>
>  	return pages;
>
> @@ -514,6 +560,7 @@ static int sev_launch_update_shared_gfn_handler(struct kvm *kvm,
>
>  	size = (range->end - range->start) << PAGE_SHIFT;
>  	vaddr_end = vaddr + size;
> +	WARN_ON(size < PAGE_SIZE);
>
>  	/* Lock the user memory. */
>  	inpages = sev_pin_memory(kvm, vaddr, size, &npages, 1);
> @@ -554,13 +601,16 @@ static int sev_launch_update_shared_gfn_handler(struct kvm *kvm,
>  	}
>
>  e_unpin:
> -	/* content of memory is updated, mark pages dirty */
> -	for (i = 0; i < npages; i++) {
> -		set_page_dirty_lock(inpages[i]);
> -		mark_page_accessed(inpages[i]);
> +	if (!kvm_is_upm_enabled(kvm)) {
> +		/* content of memory is updated, mark pages dirty */
> +		for (i = 0; i < npages; i++) {
> +			set_page_dirty_lock(inpages[i]);
> +			mark_page_accessed(inpages[i]);
> +		}
> +		/* unlock the user pages */
> +		sev_unpin_memory(kvm, inpages, npages);
>  	}
> -	/* unlock the user pages */
> -	sev_unpin_memory(kvm, inpages, npages);
> +
>  	return ret;
>  }
>
> @@ -609,9 +659,8 @@ static int sev_launch_update_priv_gfn_handler(struct kvm *kvm,
>  			goto e_ret;
>  		kvm_release_pfn_clean(pfn);
>  	}
> -	kvm_vm_set_region_attr(kvm, range->start, range->end,
> -		true /* priv_attr */);
>
> +	kvm_vm_set_region_attr(kvm, range->start, range->end, KVM_MEMORY_ATTRIBUTE_PRIVATE);
>  e_ret:
>  	return ret;
>  }
> --
> 2.25.1
>

Regards, Tom