Put the page reference acquired by gfn_to_pfn_prot() if
kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
than-stellar heuristics for dealing with pfn-mapped memory means that KVM
can get a page reference to ZONE_DEVICE memory.

Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/arm64/kvm/guest.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 11098eb7eb44..e1f0ff08836a 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
 		page = pfn_to_online_page(pfn);
 		if (!page) {
 			/* Reject ZONE_DEVICE memory */
+			kvm_release_pfn_clean(pfn);
 			ret = -EFAULT;
 			goto out;
 		}
-- 
2.46.0.rc1.232.g9752f9e123-goog

On Fri, Jul 26, 2024 at 04:51:10PM -0700, Sean Christopherson wrote:
> Put the page reference acquired by gfn_to_pfn_prot() if
> kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
> than-stellar heuristics for dealing with pfn-mapped memory means that KVM
> can get a page reference to ZONE_DEVICE memory.
> 
> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/arm64/kvm/guest.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 11098eb7eb44..e1f0ff08836a 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>  		page = pfn_to_online_page(pfn);
>  		if (!page) {
>  			/* Reject ZONE_DEVICE memory */
> +			kvm_release_pfn_clean(pfn);
>  			ret = -EFAULT;
>  			goto out;
>  		}

This patch makes sense irrespective of whether the above pfn is a
ZONE_DEVICE or not. gfn_to_pfn_prot() increased the page refcount via
GUP, so it must be released before bailing out of this loop.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

On 07/08/2024 15:15, Catalin Marinas wrote:
> On Fri, Jul 26, 2024 at 04:51:10PM -0700, Sean Christopherson wrote:
>> Put the page reference acquired by gfn_to_pfn_prot() if
>> kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
>> than-stellar heuristics for dealing with pfn-mapped memory means that KVM
>> can get a page reference to ZONE_DEVICE memory.
>>
>> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
>> Signed-off-by: Sean Christopherson <seanjc@google.com>
>> ---
>>  arch/arm64/kvm/guest.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
>> index 11098eb7eb44..e1f0ff08836a 100644
>> --- a/arch/arm64/kvm/guest.c
>> +++ b/arch/arm64/kvm/guest.c
>> @@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>>  		page = pfn_to_online_page(pfn);
>>  		if (!page) {
>>  			/* Reject ZONE_DEVICE memory */
>> +			kvm_release_pfn_clean(pfn);
>>  			ret = -EFAULT;
>>  			goto out;
>>  		}
> 
> This patch makes sense irrespective of whether the above pfn is a
> ZONE_DEVICE or not. gfn_to_pfn_prot() increased the page refcount via
> GUP, so it must be released before bailing out of this loop.
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> 

Yep, as Catalin says, this is an 'obviously' correct fix - the reference
needs releasing before bailing out. The comment there is perhaps
misleading - it's not just ZONE_DEVICE memory that will be rejected, but
this is the case that was in my mind when I wrote it. Although clearly I
wasn't thinking hard enough when writing the code in the first place... ;)

Reviewed-by: Steven Price <steven.price@arm.com>

Thanks,

Steve

+ Steven Price for this patch (and the following one), as this really
is his turf.

On Sat, 27 Jul 2024 00:51:10 +0100,
Sean Christopherson <seanjc@google.com> wrote:
> 
> Put the page reference acquired by gfn_to_pfn_prot() if
> kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
> than-stellar heuristics for dealing with pfn-mapped memory means that KVM
> can get a page reference to ZONE_DEVICE memory.
> 
> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/arm64/kvm/guest.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 11098eb7eb44..e1f0ff08836a 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>  		page = pfn_to_online_page(pfn);
>  		if (!page) {
>  			/* Reject ZONE_DEVICE memory */
> +			kvm_release_pfn_clean(pfn);
>  			ret = -EFAULT;
>  			goto out;
>  		}
> -- 
> 2.46.0.rc1.232.g9752f9e123-goog
> 
> 

-- 
Without deviation from the norm, progress is not possible.

Sean Christopherson <seanjc@google.com> writes:

> Put the page reference acquired by gfn_to_pfn_prot() if
> kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
> than-stellar heuristics for dealing with pfn-mapped memory means that KVM
> can get a page reference to ZONE_DEVICE memory.
>
> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/arm64/kvm/guest.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 11098eb7eb44..e1f0ff08836a 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>  		page = pfn_to_online_page(pfn);
>  		if (!page) {
>  			/* Reject ZONE_DEVICE memory */
> +			kvm_release_pfn_clean(pfn);

I guess this gets renamed later in the series.

However my main comment is does lack of page always mean a ZONE_DEVICE?
Looking at pfn_to_online_page() I see a bunch of other checks first. Why
isn't it that functions responsibility to clean up after itself if its
returning NULLs?

>  			ret = -EFAULT;
>  			goto out;
>  		}

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro

On Wed, Jul 31, 2024, Alex Bennée wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > Put the page reference acquired by gfn_to_pfn_prot() if
> > kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
> > than-stellar heuristics for dealing with pfn-mapped memory means that KVM
> > can get a page reference to ZONE_DEVICE memory.
> >
> > Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >  arch/arm64/kvm/guest.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> > index 11098eb7eb44..e1f0ff08836a 100644
> > --- a/arch/arm64/kvm/guest.c
> > +++ b/arch/arm64/kvm/guest.c
> > @@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
> >  		page = pfn_to_online_page(pfn);
> >  		if (!page) {
> >  			/* Reject ZONE_DEVICE memory */
> > +			kvm_release_pfn_clean(pfn);
> 
> I guess this gets renamed later in the series.
> 
> However my main comment is does lack of page always mean a ZONE_DEVICE?

Nope.

> Looking at pfn_to_online_page() I see a bunch of other checks first. Why
> isn't it that functions responsibility to clean up after itself if its
> returning NULLs?

pfn_to_online_page() is more strict than gfn_to_pfn_prot().  At least in theory,
gfn_to_pfn_prot() could return a pfn that has an associated "struct page", with
a reference held to said page.  But for that same pfn, pfn_to_online_page() could
return NULL, in which case KVM needs to put the reference it acquired via
gfn_to_pfn_prot().

On Fri, 26 Jul 2024 16:51:10 -0700, Sean Christopherson wrote:
> Put the page reference acquired by gfn_to_pfn_prot() if
> kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
> than-stellar heuristics for dealing with pfn-mapped memory means that KVM
> can get a page reference to ZONE_DEVICE memory.
> 
> 

Applied to next, thanks!

[01/84] KVM: arm64: Release pfn, i.e. put page, if copying MTE tags hits ZONE_DEVICE
        commit: ae41d7dbaeb4f79134136cd65ad7015cf9ccf78a

Cheers,

	M.
-- 
Without deviation from the norm, progress is not possible.