Re: [PATCH] KVM: s390: vsie: Check alignment of BSCA header

["Christoph Schlameuss" <schlameuss@linux.ibm.com>]

On Fri Nov 7, 2025 at 3:49 AM CET, Eric Farman wrote:
> The VSIE code currently checks that the BSCA struct fits within
> a page, and returns a validity exception 0x003b if it doesn't.
> The BSCA is pinned in memory rather than shadowed (see block
> comment at end of kvm_s390_cpu_feat_init()), so enforcing the
> CPU entries to be on the same pinned page makes sense.
>
> Except those entries aren't going to be used below the guest,
> and according to the definition of that validity exception only
> the header of the BSCA (everything but the CPU entries) needs to
> be within a page. Adjust the alignment check to account for that.
>
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
>  arch/s390/kvm/vsie.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 347268f89f2f..d23ab5120888 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -782,7 +782,7 @@ static int pin_blocks(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  		else if ((gpa & ~0x1fffUL) == kvm_s390_get_prefix(vcpu))
>  			rc = set_validity_icpt(scb_s, 0x0011U);
>  		else if ((gpa & PAGE_MASK) !=
> -			 ((gpa + sizeof(struct bsca_block) - 1) & PAGE_MASK))
> +			 ((gpa + offsetof(struct bsca_block, cpu[0]) - 1) & PAGE_MASK))

Did you test if this works with an esca, where the header is bigger than this?
Previously the esca header was covered by the whole bsca struct.

>  			rc = set_validity_icpt(scb_s, 0x003bU);
>  		if (!rc) {
>  			rc = pin_guest_page(vcpu->kvm, gpa, &hpa);