[PATCH v2] KVM: s390: gaccess: Refactor access address range check

Janis Schoetterl-Glausch
2021-10-28T13:56:57Z

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>
---
arch/s390/kvm/gaccess.c | 122 +++++++++++++++++++++++-----------------
1 file changed, 69 insertions(+), 53 deletions(-)

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 0d11cea92603..7725dd7566ed 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/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 gpas 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 nr_pages, idx;
unsigned int fragment_len;
- unsigned long pages_array[2];
- unsigned long *pages;
+ unsigned long gpa_array[2];
+ 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;
--
2.25.1