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

[Nikunj A. Dadhania]

On 22/12/22 23:54, erbse.13@xxxxxx wrote:
> On Wed, Dec 14, 2022 at 01:40:03PM -0600, Michael Roth wrote:
>> From: Nikunj A Dadhania <nikunj@xxxxxxx>
>>
>> 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@xxxxxxx>
>> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
>> ---
>>  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.

Good catch, will fix.

>> +
>>  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.

Sure, will fix.

> 
>> +	} 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

Thanks
Nikunj