KVM: s390: gaccess: Refactor access address range check

Do not round down the first address to the page boundary, just translate
it normally, which gives the value we care about in the first place.
Given this, translating a single address is just the special case of
translating a range spanning a single page.

Make the output optional, so the function can be used to just check a
range.
Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20211126164549.7046-3-scgl@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

arch/s390/kvm/gaccess.c

@@ -794,35 +794,74 @@ static int low_address_protection_enabled(struct kvm_vcpu *vcpu,
 	return 1;
 }
 
-static int guest_page_range(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
-			    unsigned long *pages, unsigned long nr_pages,
-			    const union asce asce, enum gacc_mode mode)
+/**
+ * guest_range_to_gpas() - Calculate guest physical addresses of page fragments
+ * covering a logical range
+ * @vcpu: virtual cpu
+ * @ga: guest address, start of range
+ * @ar: access register
+ * @gpas: output argument, may be NULL
+ * @len: length of range in bytes
+ * @asce: address-space-control element to use for translation
+ * @mode: access mode
+ *
+ * Translate a logical range to a series of guest absolute addresses,
+ * such that the concatenation of page fragments starting at each gpa make up
+ * the whole range.
+ * The translation is performed as if done by the cpu for the given @asce, @ar,
+ * @mode and state of the @vcpu.
+ * If the translation causes an exception, its program interruption code is
+ * returned and the &struct kvm_s390_pgm_info pgm member of @vcpu is modified
+ * such that a subsequent call to kvm_s390_inject_prog_vcpu() will inject
+ * a correct exception into the guest.
+ * The resulting gpas are stored into @gpas, unless it is NULL.
+ *
+ * Note: All fragments except the first one start at the beginning of a page.
+ *	 When deriving the boundaries of a fragment from a gpa, all but the last
+ *	 fragment end at the end of the page.
+ *
+ * Return:
+ * * 0		- success
+ * * <0		- translation could not be performed, for example if  guest
+ *		  memory could not be accessed
+ * * >0		- an access exception occurred. In this case the returned value
+ *		  is the program interruption code and the contents of pgm may
+ *		  be used to inject an exception into the guest.
+ */
+static int guest_range_to_gpas(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
+			       unsigned long *gpas, unsigned long len,
+			       const union asce asce, enum gacc_mode mode)
 {
 	psw_t *psw = &vcpu->arch.sie_block->gpsw;
+	unsigned int offset = offset_in_page(ga);
+	unsigned int fragment_len;
 	int lap_enabled, rc = 0;
 	enum prot_type prot;
+	unsigned long gpa;
 
 	lap_enabled = low_address_protection_enabled(vcpu, asce);
-	while (nr_pages) {
+	while (min(PAGE_SIZE - offset, len) > 0) {
+		fragment_len = min(PAGE_SIZE - offset, len);
 		ga = kvm_s390_logical_to_effective(vcpu, ga);
 		if (mode == GACC_STORE && lap_enabled && is_low_address(ga))
 			return trans_exc(vcpu, PGM_PROTECTION, ga, ar, mode,
 					 PROT_TYPE_LA);
-		ga &= PAGE_MASK;
 		if (psw_bits(*psw).dat) {
-			rc = guest_translate(vcpu, ga, pages, asce, mode, &prot);
+			rc = guest_translate(vcpu, ga, &gpa, asce, mode, &prot);
 			if (rc < 0)
 				return rc;
 		} else {
-			*pages = kvm_s390_real_to_abs(vcpu, ga);
-			if (kvm_is_error_gpa(vcpu->kvm, *pages))
+			gpa = kvm_s390_real_to_abs(vcpu, ga);
+			if (kvm_is_error_gpa(vcpu->kvm, gpa))
 				rc = PGM_ADDRESSING;
 		}
 		if (rc)
 			return trans_exc(vcpu, rc, ga, ar, mode, prot);
-		ga += PAGE_SIZE;
-		pages++;
-		nr_pages--;
+		if (gpas)
+			*gpas++ = gpa;
+		offset = 0;
+		ga += fragment_len;
+		len -= fragment_len;
 	}
 	return 0;
 }
@@ -831,10 +870,10 @@ int access_guest(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, void *data,
 		 unsigned long len, enum gacc_mode mode)
 {
 	psw_t *psw = &vcpu->arch.sie_block->gpsw;
-	unsigned long nr_pages, gpa, idx;
-	unsigned long pages_array[2];
+	unsigned long nr_pages, idx;
+	unsigned long gpa_array[2];
 	unsigned int fragment_len;
-	unsigned long *pages;
+	unsigned long *gpas;
 	int need_ipte_lock;
 	union asce asce;
 	int rc;
@@ -846,30 +885,28 @@ int access_guest(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, void *data,
 	if (rc)
 		return rc;
 	nr_pages = (((ga & ~PAGE_MASK) + len - 1) >> PAGE_SHIFT) + 1;
-	pages = pages_array;
-	if (nr_pages > ARRAY_SIZE(pages_array))
-		pages = vmalloc(array_size(nr_pages, sizeof(unsigned long)));
-	if (!pages)
+	gpas = gpa_array;
+	if (nr_pages > ARRAY_SIZE(gpa_array))
+		gpas = vmalloc(array_size(nr_pages, sizeof(unsigned long)));
+	if (!gpas)
 		return -ENOMEM;
 	need_ipte_lock = psw_bits(*psw).dat && !asce.r;
 	if (need_ipte_lock)
 		ipte_lock(vcpu);
-	rc = guest_page_range(vcpu, ga, ar, pages, nr_pages, asce, mode);
+	rc = guest_range_to_gpas(vcpu, ga, ar, gpas, len, asce, mode);
 	for (idx = 0; idx < nr_pages && !rc; idx++) {
-		gpa = pages[idx] + offset_in_page(ga);
-		fragment_len = min(PAGE_SIZE - offset_in_page(gpa), len);
+		fragment_len = min(PAGE_SIZE - offset_in_page(gpas[idx]), len);
 		if (mode == GACC_STORE)
-			rc = kvm_write_guest(vcpu->kvm, gpa, data, fragment_len);
+			rc = kvm_write_guest(vcpu->kvm, gpas[idx], data, fragment_len);
 		else
-			rc = kvm_read_guest(vcpu->kvm, gpa, data, fragment_len);
+			rc = kvm_read_guest(vcpu->kvm, gpas[idx], data, fragment_len);
 		len -= fragment_len;
-		ga += fragment_len;
 		data += fragment_len;
 	}
 	if (need_ipte_lock)
 		ipte_unlock(vcpu);
-	if (nr_pages > ARRAY_SIZE(pages_array))
-		vfree(pages);
+	if (nr_pages > ARRAY_SIZE(gpa_array))
+		vfree(gpas);
 	return rc;
 }
 
@@ -911,8 +948,6 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
 int guest_translate_address(struct kvm_vcpu *vcpu, unsigned long gva, u8 ar,
 			    unsigned long *gpa, enum gacc_mode mode)
 {
-	psw_t *psw = &vcpu->arch.sie_block->gpsw;
-	enum prot_type prot;
 	union asce asce;
 	int rc;
 
@@ -920,23 +955,7 @@ int guest_translate_address(struct kvm_vcpu *vcpu, unsigned long gva, u8 ar,
 	rc = get_vcpu_asce(vcpu, &asce, gva, ar, mode);
 	if (rc)
 		return rc;
-	if (is_low_address(gva) && low_address_protection_enabled(vcpu, asce)) {
-		if (mode == GACC_STORE)
-			return trans_exc(vcpu, PGM_PROTECTION, gva, 0,
-					 mode, PROT_TYPE_LA);
-	}
-
-	if (psw_bits(*psw).dat && !asce.r) {	/* Use DAT? */
-		rc = guest_translate(vcpu, gva, gpa, asce, mode, &prot);
-		if (rc > 0)
-			return trans_exc(vcpu, rc, gva, 0, mode, prot);
-	} else {
-		*gpa = kvm_s390_real_to_abs(vcpu, gva);
-		if (kvm_is_error_gpa(vcpu->kvm, *gpa))
-			return trans_exc(vcpu, rc, gva, PGM_ADDRESSING, mode, 0);
-	}
-
-	return rc;
+	return guest_range_to_gpas(vcpu, gva, ar, gpa, 1, asce, mode);
 }
 
 /**
@@ -950,17 +969,14 @@ int guest_translate_address(struct kvm_vcpu *vcpu, unsigned long gva, u8 ar,
 int check_gva_range(struct kvm_vcpu *vcpu, unsigned long gva, u8 ar,
 		    unsigned long length, enum gacc_mode mode)
 {
-	unsigned long gpa;
-	unsigned long currlen;
+	union asce asce;
 	int rc = 0;
 
+	rc = get_vcpu_asce(vcpu, &asce, gva, ar, mode);
+	if (rc)
+		return rc;
 	ipte_lock(vcpu);
-	while (length > 0 && !rc) {
-		currlen = min(length, PAGE_SIZE - (gva % PAGE_SIZE));
-		rc = guest_translate_address(vcpu, gva, ar, &gpa, mode);
-		gva += currlen;
-		length -= currlen;
-	}
+	rc = guest_range_to_gpas(vcpu, gva, ar, NULL, length, asce, mode);
 	ipte_unlock(vcpu);
 
 	return rc;