linux-kernel - Re: [PATCH v1 07/11] KVM: s390: pv: add export before import

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Date:   Wed, 26 May 2021 13:56:58 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     cohuck@...hat.com, borntraeger@...ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, david@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 07/11] KVM: s390: pv: add export before import

On 5/17/21 10:07 PM, Claudio Imbrenda wrote:
> Due to upcoming changes, it will be possible to temporarily have
> multiple protected VMs in the same address space. When that happens,
> it is necessary to perform an export of every page that is to be
> imported.

... since the Ultravisor doesn't allow KVM to import a secure page
belonging to guest A to be imported for guest B in order to guarantee
proper guest isolation.

Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>

> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
>  arch/s390/kernel/uv.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index b19b1a1444ec..dbcf4434eb53 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -242,6 +242,12 @@ static int make_secure_pte(pte_t *ptep, unsigned long addr,
>  	return rc;
>  }
>  
> +static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_struct *mm)
> +{
> +	return uvcb->cmd != UVC_CMD_UNPIN_PAGE_SHARED &&
> +		atomic_read(&mm->context.is_protected) > 1;
> +}
> +
>  /*
>   * Requests the Ultravisor to make a page accessible to a guest.
>   * If it's brought in the first time, it will be cleared. If
> @@ -285,6 +291,8 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
>  
>  	lock_page(page);
>  	ptep = get_locked_pte(gmap->mm, uaddr, &ptelock);
> +	if (should_export_before_import(uvcb, gmap->mm))
> +		uv_convert_from_secure(page_to_phys(page));
>  	rc = make_secure_pte(ptep, uaddr, page, uvcb);
>  	pte_unmap_unlock(ptep, ptelock);
>  	unlock_page(page);
>