Commit 232b8e3b authored Mar 31, 2017 by Heiko Carstens Committed by Christian Borntraeger Apr 03, 2017

KVM: s390: remove change-recording override support



Change-recording override (CO) was never implemented in any
machine. According to the architecture it is unpredictable if a
translation-specification exception will be recognized if the bit is
set and EDAT1 does not apply.
Therefore the easiest solution is to simply ignore the bit.

This also fixes commit cd1836f5 ("KVM: s390:
instruction-execution-protection support"). A guest may enable
instruction-execution-protection (IEP) but not EDAT1. In such a case
the guest_translate() function (arch/s390/kvm/gaccess.c) will report a
specification exception on pages that have the IEP bit set while it
should not.

It might make sense to add full IEP support to guest_translate() and
the GACC_IFETCH case. However, as far as I can tell the GACC_IFETCH
case is currently only used after an instruction was executed in order
to fetch the failing instruction. So there is no additional problem
*currently*.

Fixes: cd1836f5 ("KVM: s390: instruction-execution-protection support")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

parent 97da3854

arch/s390/kvm/gaccess.c

+2 −5

Original line number	Diff line number	Diff line
		@@ -168,8 +168,7 @@ union page_table_entry {
		unsigned long z : 1; /* Zero Bit */
		unsigned long i : 1; /* Page-Invalid Bit */
		unsigned long p : 1; /* DAT-Protection Bit */
		unsigned long co : 1; /* Change-Recording Override */
		unsigned long : 8;
		unsigned long : 9;
		};
		};

		@@ -745,8 +744,6 @@ static unsigned long guest_translate(struct kvm_vcpu *vcpu, unsigned long gva,
		return PGM_PAGE_TRANSLATION;
		if (pte.z)
		return PGM_TRANSLATION_SPEC;
		if (pte.co && !edat1)
		return PGM_TRANSLATION_SPEC;
		dat_protection \|= pte.p;
		raddr.pfra = pte.pfra;
		real_address:
		@@ -1182,7 +1179,7 @@ int kvm_s390_shadow_fault(struct kvm_vcpu vcpu, struct gmap sg,
		rc = gmap_read_table(sg->parent, pgt + vaddr.px * 8, &pte.val);
		if (!rc && pte.i)
		rc = PGM_PAGE_TRANSLATION;
		if (!rc && (pte.z \|\| (pte.co && sg->edat_level < 1)))
		if (!rc && pte.z)
		rc = PGM_TRANSLATION_SPEC;
		shadow_page:
		pte.p \|= dat_protection;

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