linux-kernel - Re: [PATCH v6 03/17] KVM: s390: pv: handle secure storage exceptions for normal guests

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Date:   Thu, 13 Jan 2022 10:58:26 +0100
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 v6 03/17] KVM: s390: pv: handle secure storage exceptions
 for normal guests

On 12/3/21 17:58, Claudio Imbrenda wrote:
> With upcoming patches, normal guests might touch secure pages.
> 
> This patch extends the existing exception handler to convert the pages
> to non secure also when the exception is triggered by a normal guest.
> 
> This can happen for example when a secure guest reboots; the first
> stage of a secure guest is non secure, and in general a secure guest
> can reboot into non-secure mode.
> 
> If the secure memory of the previous boot has not been cleared up
> completely yet (which will be allowed to happen in an upcoming patch),
> a non-secure guest might touch secure memory, which will need to be
> handled properly.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
>   arch/s390/mm/fault.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index a1928c89bbfa..a644e593eef9 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -770,6 +770,7 @@ void do_secure_storage_access(struct pt_regs *regs)
>   	struct vm_area_struct *vma;
>   	struct mm_struct *mm;
>   	struct page *page;
> +	struct gmap *gmap;
>   	int rc;
>   
>   	/*
> @@ -799,6 +800,14 @@ void do_secure_storage_access(struct pt_regs *regs)
>   	}
>   
>   	switch (get_fault_type(regs)) {
> +	case GMAP_FAULT:
> +		gmap = (struct gmap *)S390_lowcore.gmap;
> +		addr = __gmap_translate(gmap, addr);

__gmap_translate() needs the mmap_read_lock(mm), no?

> +		if (IS_ERR_VALUE(addr)) {
> +			do_fault_error(regs, VM_ACCESS_FLAGS, VM_FAULT_BADMAP);
> +			break;
> +		}
> +		fallthrough;
>   	case USER_FAULT:
>   		mm = current->mm;
>   		mmap_read_lock(mm);
> @@ -827,7 +836,6 @@ void do_secure_storage_access(struct pt_regs *regs)
>   		if (rc)
>   			BUG();
>   		break;
> -	case GMAP_FAULT:
>   	default:
>   		do_fault_error(regs, VM_READ | VM_WRITE, VM_FAULT_BADMAP);
>   		WARN_ON_ONCE(1);
>