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Mon, 20 Jul 2026 08:58:35 +0000 (GMT) Received: from tuxmaker.boeblingen.de.ibm.com (unknown [9.87.85.9]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 20 Jul 2026 08:58:34 +0000 (GMT) From: Heiko Carstens To: Alexander Gordeev , Sven Schnelle , Vasily Gorbik , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , David Hildenbrand Cc: linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 1/8] KVM: s390: pv: Use VM_SPARSE area for guest variable storage area Date: Mon, 20 Jul 2026 10:58:27 +0200 Message-ID: <20260720085834.898025-2-hca@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260720085834.898025-1-hca@linux.ibm.com> References: <20260720085834.898025-1-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=HJXz0Itv c=1 sm=1 tr=0 ts=6a5de340 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=CGB7rVRhuG4dzmKA8wAA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzIwMDA5NiBTYWx0ZWRfX4tl8s//KLyTd PS+5wnZ+Y+xcxn3f5V6cuLzSfSFRwYaSNS/egQte3Ajx4jFeiqraFVrr2QiIGJnEZU8oBxyrpPB y8ep/mczl2LXqSVxSNBdAYZ72xi157IBExlelZ92fmZnNA+AE5cq+tpoy8y5Xn8HT4RVfquDI/K oATNTA0bufTBYM9ECf9uyDK/hGNjfND1MNHUB2zG18BBwHtWZRZGicSdN6qqzMEHu53RXWAtScc cherIHG+X+3fRmBn5+YMrlXxgCq3UYKF8tdHzpn06yyweR9os/KlEzlhdZnksbguIh5wvh0oswS dYsm5TDFa1xRkzlmCUnwR3qW8qo3Wx7pBUi5Kg07KaFUOZX9KzDYAsHfcHeCC+t6dU0GANAzvf3 4nA9ZFmFEG5CZ867XPxDxeJX7Hj9N2qiZ2DJ5+xV43egqy3lkAqSlZNt21T4ZI8GyEGRyrdJN31 7s/eZx+rBnWnBxf8rvw== X-Proofpoint-ORIG-GUID: -S37DKE_Uy8BRsi6Nmb8Y9W-HajXkfnP X-Proofpoint-Spam-Info: AW1haW4tMjYwNzIwMDA5NiBTYWx0ZWRfX+Thkimt62m4k 9heT6rTy+5VB1UhsWMCkwXQr4AforcqR0iqbx36VKc5/qSW1aanAXk2o+Unei/N+8NMs2AJj1bQ 8aFvFH4Q9jbnoyC0GVP+Vte/5skoCDI= X-Proofpoint-GUID: -S37DKE_Uy8BRsi6Nmb8Y9W-HajXkfnP X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-20_01,2026-07-17_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 suspectscore=0 malwarescore=0 impostorscore=0 clxscore=1015 phishscore=0 spamscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607200096 The guest variable storage area is allocated with vmalloc and then donated to the ultravisor. Any kernel access to that area will result in a secure storage access exception (aka fault). This is a problem if such a memory area is read via /proc/kcore. This causes an exception via vread_iter() and results in an unexpected short read. Avoid this by allocating a custom VM_SPARSE area. If such an area is read, vread_iter() returns zeroes for the entire area. Note that the function which frees the area does not update ptes. This is intentional to allow for deferred / lazy pte updates and TLB flushing like the generic vfree() code is doing that. See vunmap_pte_range(). This assumes that s390 will gain full support for lazy_mmu_mode_enable() and lazy_mmu_mode_disable() in the future, since as of now the used ptep_get_and_clear() in vunmap_pte_range() does indeed invalidate and flush every single pte entry, but only for s390. Tested-by: Christian Borntraeger Signed-off-by: Heiko Carstens --- arch/s390/include/asm/uv.h | 2 ++ arch/s390/kernel/uv.c | 65 ++++++++++++++++++++++++++++++++++++++ arch/s390/kvm/pv.c | 6 ++-- 3 files changed, 70 insertions(+), 3 deletions(-) diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h index d919e69662f5..153fed63adda 100644 --- a/arch/s390/include/asm/uv.h +++ b/arch/s390/include/asm/uv.h @@ -635,6 +635,8 @@ int s390_wiggle_split_folio(struct mm_struct *mm, struct folio *folio); int __make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb); int uv_convert_from_secure(unsigned long paddr); int uv_convert_from_secure_folio(struct folio *folio); +void *uv_alloc_stor_var(unsigned long size); +void uv_free_stor_var(void *stor_var); void setup_uv(void); diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c index a284f98d9716..d1cdc5ae5e27 100644 --- a/arch/s390/kernel/uv.c +++ b/arch/s390/kernel/uv.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include #include @@ -209,6 +210,70 @@ int uv_convert_from_secure_pte(pte_t pte) return uv_convert_from_secure_folio(pfn_folio(pte_pfn(pte))); } +static int uv_free_range_cb(pte_t *ptep, unsigned long addr, void *data) +{ + pte_t pte = ptep_get(ptep); + + if (!pte_present(pte)) + return 0; + /* + * Note: do not update the pte here, since there is no code which + * accesses the memory range, besides bugs. The invalidation of ptes + * and TLB flushing is deferred like for regular vfree() calls. + */ + __free_page(pte_page(pte)); + return 0; +} + +void uv_free_stor_var(void *stor_var) +{ + unsigned long addr, size; + struct vm_struct *area; + + if (!stor_var) + return; + area = find_vm_area(stor_var); + if (WARN_ON_ONCE(!area || !(area->flags & VM_SPARSE))) + return; + size = get_vm_area_size(area); + addr = (unsigned long)area->addr; + apply_to_existing_page_range(&init_mm, addr, size, uv_free_range_cb, NULL); + free_vm_area(area); +} +EXPORT_SYMBOL_FOR_MODULES(uv_free_stor_var, "kvm"); + +static int uv_alloc_range_cb(pte_t *ptep, unsigned long addr, void *data) +{ + struct page *page; + pte_t pte; + + page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO); + if (!page) + return -ENOMEM; + pte = __pte(page_to_phys(page) | pgprot_val(PAGE_KERNEL)); + set_pte(ptep, pte); + return 0; +} + +void *uv_alloc_stor_var(unsigned long size) +{ + struct vm_struct *area; + unsigned long addr; + + size = PAGE_ALIGN(size); + area = get_vm_area(size, VM_SPARSE); + if (!area) + return NULL; + addr = (unsigned long)area->addr; + if (apply_to_page_range(&init_mm, addr, size, uv_alloc_range_cb, NULL)) + goto out; + return area->addr; +out: + uv_free_stor_var(area->addr); + return NULL; +} +EXPORT_SYMBOL_FOR_MODULES(uv_alloc_stor_var, "kvm"); + /* * Calculate the expected ref_count for a folio that would otherwise have no * further pins. This was cribbed from similar functions in other places in diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c index 1beacc841ca8..dc5ac29b4c31 100644 --- a/arch/s390/kvm/pv.c +++ b/arch/s390/kvm/pv.c @@ -337,7 +337,7 @@ int kvm_s390_pv_create_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc) /* only free resources when the destroy was successful */ static void kvm_s390_pv_dealloc_vm(struct kvm *kvm) { - vfree(kvm->arch.pv.stor_var); + uv_free_stor_var(kvm->arch.pv.stor_var); free_pages(kvm->arch.pv.stor_base, get_order(uv_info.guest_base_stor_len)); kvm_s390_clear_pv_state(kvm); @@ -369,7 +369,7 @@ static int kvm_s390_pv_alloc_vm(struct kvm *kvm) /* Allocate variable storage */ vlen = ALIGN(virt * ((npages * PAGE_SIZE) / HPAGE_SIZE), PAGE_SIZE); vlen += uv_info.guest_virt_base_stor_len; - kvm->arch.pv.stor_var = vzalloc(vlen); + kvm->arch.pv.stor_var = uv_alloc_stor_var(vlen); if (!kvm->arch.pv.stor_var) goto out_err; return 0; @@ -414,7 +414,7 @@ static int kvm_s390_pv_dispose_one_leftover(struct kvm *kvm, */ free_pages(leftover->stor_base, get_order(uv_info.guest_base_stor_len)); free_pages(leftover->old_gmap_table, CRST_ALLOC_ORDER); - vfree(leftover->stor_var); + uv_free_stor_var(leftover->stor_var); done_fast: atomic_dec(&kvm->mm->context.protected_count); return 0; -- 2.53.0