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Thu, 16 Jul 2026 14:14:37 +0000 (GMT) Received: from tuxmaker.boeblingen.de.ibm.com (unknown [9.87.85.9]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 16 Jul 2026 14:14:37 +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 1/4] KVM: s390: pv: Use VM_SPARSE area for guest variable storage area Date: Thu, 16 Jul 2026 16:14:33 +0200 Message-ID: <20260716141436.2125703-2-hca@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260716141436.2125703-1-hca@linux.ibm.com> References: <20260716141436.2125703-1-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: quoted-printable X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=fOcJG5ae c=1 sm=1 tr=0 ts=6a58e751 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=P87cTALPzO2HOiDMc2MA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzE2MDE0NiBTYWx0ZWRfX9bZTvNgVTG8q 7RZjA0Fydb6fJ1GSMrPP/gVijynmweacI1Y0q+y6JIaQh7D6dWQqf0slX61cVX0KuPx+rBVFW7p qukGwAXBrJtvpsWGt0vn8H7hx/uCtIeXd1J0qawHrsfQKlMwiycHiUsp9RNcs0aOmHIddZ+XYM3 RL/HFuJXGEheyfCyM1mQWKuOiGsrhS3WeG+pwSIlLFXZuUJ4FPOhMztPsXFm4+YHXRwnrmBbC6I mW0/2rBYx5yXEzsJRzN4/pWQRzLQ47pqtF/irwuUli8791IgL1tr8DfxasD6o9Rp7dUF3ofPJj2 FdE2MMY9+jNmOu/IQ7ptUUrqrgq3G5jDD/eTLjSERJYqG9rx37cYcVSWq0ODmdjrN8rDBfdOGfR BNShbNSzAwvhr1+tYX0Dg46sK9MI+PktdYrji82yLmXuv+9tKc28gxiEXO69GOyOWnLgplq+AHF 939WMt68QcmqyUfBfvw== X-Proofpoint-Spam-Info: AW1haW4tMjYwNzE2MDE0NiBTYWx0ZWRfXyEAZKbta7sOI aJF9YEI4wOZtOCoVRkNdImEqTj6kI8Q0+Aq1P0Dq/3azcQ1babOQzko11rQA+Z4V6o+rCZqrZai TmKgkTVayZ7dSvfWrL3PCIlnOjKUFDo= X-Proofpoint-GUID: oUjZppr6snkjGMylRf9G11OhUKEVsNTm X-Proofpoint-ORIG-GUID: oUjZppr6snkjGMylRf9G11OhUKEVsNTm 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=2026-07-16_05,2026-07-15_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 impostorscore=0 suspectscore=0 adultscore=0 priorityscore=1501 malwarescore=0 clxscore=1011 phishscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607160146 Content-Type: text/plain; charset="utf-8" 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. Signed-off-by: Heiko Carstens Tested-by: Christian Borntraeger --- arch/s390/include/asm/uv.h | 2 ++ arch/s390/kernel/uv.c | 59 ++++++++++++++++++++++++++++++++++++++ arch/s390/kvm/pv.c | 6 ++-- 3 files changed, 64 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, struc= t 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); =20 void setup_uv(void); =20 diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c index a284f98d9716..98a7f988fc69 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 +210,64 @@ int uv_convert_from_secure_pte(pte_t pte) return uv_convert_from_secure_folio(pfn_folio(pte_pfn(pte))); } =20 +static int uv_free_range_cb(pte_t *ptep, unsigned long addr, void *data) +{ + pte_t pte =3D ptep_get(ptep); + + if (!pte_present(pte)) + return 0; + __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 =3D find_vm_area(stor_var); + if (WARN_ON_ONCE(!area || !(area->flags & VM_SPARSE))) + return; + size =3D get_vm_area_size(area); + addr =3D (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 =3D alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO); + if (!page) + return -ENOMEM; + pte =3D __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; + + area =3D get_vm_area(size, VM_SPARSE); + if (!area) + return NULL; + addr =3D (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 =3D ALIGN(virt * ((npages * PAGE_SIZE) / HPAGE_SIZE), PAGE_SIZE); vlen +=3D uv_info.guest_virt_base_stor_len; - kvm->arch.pv.stor_var =3D vzalloc(vlen); + kvm->arch.pv.stor_var =3D 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)); 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charset="utf-8" Secure storage access exceptions in vmalloc area need to be handled separately since folio_try_get() or virt_to_phys() do not work on such addresses. Given that there cannot be a valid access let such exceptions fail immediately. The kernel will either fixup or crash. Signed-off-by: Heiko Carstens Tested-by: Christian Borntraeger --- arch/s390/mm/fault.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c index 028aeb9c48d6..392e46742039 100644 --- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -438,6 +438,8 @@ void do_secure_storage_access(struct pt_regs *regs) panic("Unexpected PGM 0x3d with TEID bit 61=3D0"); } if (is_kernel_fault(regs)) { + if (is_vmalloc_addr((void *)addr)) + return handle_fault_error_nolock(regs, 0); folio =3D virt_to_folio((void *)addr); if (unlikely(!folio_try_get(folio))) return; --=20 2.53.0 From nobody Sat Jul 25 15:51:09 2026 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 447E23F482E; Thu, 16 Jul 2026 14:14:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal: i=1; 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charset="utf-8" Remove folio handling for secure storage access exceptions that happen via the kernel mapping. Using folio_try_get() for exceptions via the kernel mapping is racy: for example such an exception may happen on one CPU, while a different CPU frees the corresponding page. Subsequently the page can be part of a folio of different size, before the faulting CPU executes folio_try_get(). This may lead to data corruption. As of now this scenario does not seem to be possible, however with the upcoming load_unaligned_zeropad() this is possible. As a side effect PG_arch_1 is not cleared anymore for such faults via the kernel mapping. However given that this bit is over-indicating it shouldn't matter. Signed-off-by: Heiko Carstens Tested-by: Christian Borntraeger --- arch/s390/mm/fault.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c index 392e46742039..db77c8c0023e 100644 --- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -440,13 +440,7 @@ void do_secure_storage_access(struct pt_regs *regs) if (is_kernel_fault(regs)) { if (is_vmalloc_addr((void *)addr)) return handle_fault_error_nolock(regs, 0); - folio =3D virt_to_folio((void *)addr); - if (unlikely(!folio_try_get(folio))) - return; - rc =3D uv_convert_from_secure(folio_to_phys(folio)); - if (!rc) - clear_bit(PG_arch_1, &folio->flags.f); - folio_put(folio); + rc =3D uv_convert_from_secure(__pa(addr)); /* * There are some valid fixup types for kernel * accesses to donated secure memory. zeropad is one --=20 2.53.0 From nobody Sat Jul 25 15:51:09 2026 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 447423F0774; 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charset="utf-8" Implement load_unaligned_zeropad() and enable DCACHE_WORD_ACCESS to speed up string operations in fs/dcache.c and fs/namei.c. With the secure storage access exception cases addressed, add support for DCACHE_WORD_ACCESS again. Signed-off-by: Heiko Carstens Tested-by: Christian Borntraeger --- arch/s390/Kconfig | 1 + arch/s390/include/asm/asm-extable.h | 4 ++++ arch/s390/include/asm/word-at-a-time.h | 22 ++++++++++++++++++++++ arch/s390/mm/extable.c | 18 ++++++++++++++++++ 4 files changed, 45 insertions(+) diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig index 84404e6778d5..fe81c539ef2f 100644 --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -163,6 +163,7 @@ config S390 select ARCH_WANTS_THP_SWAP select BUILDTIME_TABLE_SORT select CLONE_BACKWARDS2 + select DCACHE_WORD_ACCESS if !KMSAN select DYNAMIC_FTRACE if FUNCTION_TRACER select FUNCTION_ALIGNMENT_8B if CC_IS_GCC select FUNCTION_ALIGNMENT_16B if !CC_IS_GCC diff --git a/arch/s390/include/asm/asm-extable.h b/arch/s390/include/asm/as= m-extable.h index 99748c20e767..d23ea0c94e4e 100644 --- a/arch/s390/include/asm/asm-extable.h +++ b/arch/s390/include/asm/asm-extable.h @@ -12,6 +12,7 @@ #define EX_TYPE_UA_FAULT 3 #define EX_TYPE_UA_LOAD_REG 5 #define EX_TYPE_UA_LOAD_REGPAIR 6 +#define EX_TYPE_ZEROPAD 7 #define EX_TYPE_FPC 8 #define EX_TYPE_UA_MVCOS_TO 9 #define EX_TYPE_UA_MVCOS_FROM 10 @@ -79,6 +80,9 @@ #define EX_TABLE_UA_LOAD_REGPAIR(_fault, _target, _regerr, _regzero) \ __EX_TABLE(__ex_table, _fault, _target, EX_TYPE_UA_LOAD_REGPAIR, _regerr,= _regzero, 0) =20 +#define EX_TABLE_ZEROPAD(_fault, _target, _regdata, _regaddr) \ + __EX_TABLE(__ex_table, _fault, _target, EX_TYPE_ZEROPAD, _regdata, _regad= dr, 0) + #define EX_TABLE_FPC(_fault, _target) \ __EX_TABLE(__ex_table, _fault, _target, EX_TYPE_FPC, __stringify(%%r0), _= _stringify(%%r0), 0) =20 diff --git a/arch/s390/include/asm/word-at-a-time.h b/arch/s390/include/asm= /word-at-a-time.h index e9287036392d..eaa19dee7699 100644 --- a/arch/s390/include/asm/word-at-a-time.h +++ b/arch/s390/include/asm/word-at-a-time.h @@ -4,6 +4,7 @@ =20 #include #include +#include #include =20 struct word_at_a_time { @@ -40,4 +41,25 @@ static inline unsigned long zero_bytemask(unsigned long = data) return ~1UL << data; } =20 +/* + * Load an unaligned word from kernel space. + * + * In the (very unlikely) case of the word being a page-crosser + * and the next page not being mapped, take the exception and + * return zeroes in the non-existing part. + */ +static inline unsigned long load_unaligned_zeropad(const void *addr) +{ + unsigned long data; + + asm_inline volatile( + "0: lg %[data],0(%[addr])\n" + "1: nopr %%r7\n" + EX_TABLE_ZEROPAD(0b, 1b, %[data], %[addr]) + EX_TABLE_ZEROPAD(1b, 1b, %[data], %[addr]) + : [data] "=3Dd" (data) + : [addr] "a" (addr), "m" (*(unsigned long *)addr)); + return data; +} + #endif /* _ASM_WORD_AT_A_TIME_H */ diff --git a/arch/s390/mm/extable.c b/arch/s390/mm/extable.c index 063b4346742d..7498e858c401 100644 --- a/arch/s390/mm/extable.c +++ b/arch/s390/mm/extable.c @@ -50,6 +50,22 @@ static bool ex_handler_ua_load_reg(const struct exceptio= n_table_entry *ex, return true; } =20 +static bool ex_handler_zeropad(const struct exception_table_entry *ex, str= uct pt_regs *regs) +{ + unsigned int reg_addr =3D FIELD_GET(EX_DATA_REG_ADDR, ex->data); + unsigned int reg_data =3D FIELD_GET(EX_DATA_REG_ERR, ex->data); + unsigned long data, addr, offset; + + addr =3D regs->gprs[reg_addr]; + offset =3D addr & (sizeof(unsigned long) - 1); + addr &=3D ~(sizeof(unsigned long) - 1); + data =3D *(unsigned long *)addr; + data <<=3D BITS_PER_BYTE * offset; + regs->gprs[reg_data] =3D data; + regs->psw.addr =3D extable_fixup(ex); + return true; +} + static bool ex_handler_fpc(const struct exception_table_entry *ex, struct = pt_regs *regs) { fpu_sfpc(0); @@ -118,6 +134,8 @@ bool fixup_exception(struct pt_regs *regs) return ex_handler_ua_load_reg(ex, false, regs); case EX_TYPE_UA_LOAD_REGPAIR: return ex_handler_ua_load_reg(ex, true, regs); + case EX_TYPE_ZEROPAD: + return ex_handler_zeropad(ex, regs); case EX_TYPE_FPC: return ex_handler_fpc(ex, regs); case EX_TYPE_UA_MVCOS_TO: --=20 2.53.0