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

Janosch Frank
2021-11-19T08:56:26Z

On 10/28/21 15:55, Janis Schoetterl-Glausch wrote:
> 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>

> ---
> 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

I'd add an empty line here.
Apart from that this is a very nice cleanup.

> + * @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;
>