s390 updates for 6.10-rc3

- Do not create PT_LOAD program header for the kenel image when
   the virtual memory informaton in OS_INFO data is not available.
   That fixes stand-alone dump failures against kernels that do not
   provide the virtual memory informaton
 
 - Add KVM s390 shared zeropage selftest
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Merge tag 's390-6.10-3' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

Pull s390 fixes from Alexander Gordeev:

 - Do not create PT_LOAD program header for the kenel image when the
   virtual memory informaton in OS_INFO data is not available. That
   fixes stand-alone dump failures against kernels that do not provide
   the virtual memory informaton

 - Add KVM s390 shared zeropage selftest

* tag 's390-6.10-3' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux:
  KVM: s390x: selftests: Add shared zeropage test
  s390/crash: Do not use VM info if os_info does not have it

arch/s390/kernel/crash_dump.c

@@ -451,7 +451,7 @@ static void *nt_final(void *ptr)
 /*
  * Initialize ELF header (new kernel)
  */
-static void *ehdr_init(Elf64_Ehdr *ehdr, int mem_chunk_cnt)
+static void *ehdr_init(Elf64_Ehdr *ehdr, int phdr_count)
 {
 	memset(ehdr, 0, sizeof(*ehdr));
 	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
@@ -465,11 +465,8 @@ static void *ehdr_init(Elf64_Ehdr *ehdr, int mem_chunk_cnt)
 	ehdr->e_phoff = sizeof(Elf64_Ehdr);
 	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
 	ehdr->e_phentsize = sizeof(Elf64_Phdr);
-	/*
-	 * Number of memory chunk PT_LOAD program headers plus one kernel
-	 * image PT_LOAD program header plus one PT_NOTE program header.
-	 */
-	ehdr->e_phnum = mem_chunk_cnt + 1 + 1;
+	/* Number of PT_LOAD program headers plus PT_NOTE program header */
+	ehdr->e_phnum = phdr_count + 1;
 	return ehdr + 1;
 }
 
@@ -503,12 +500,14 @@ static int get_mem_chunk_cnt(void)
 /*
  * Initialize ELF loads (new kernel)
  */
-static void loads_init(Elf64_Phdr *phdr)
+static void loads_init(Elf64_Phdr *phdr, bool os_info_has_vm)
 {
-	unsigned long old_identity_base = os_info_old_value(OS_INFO_IDENTITY_BASE);
+	unsigned long old_identity_base = 0;
 	phys_addr_t start, end;
 	u64 idx;
 
+	if (os_info_has_vm)
+		old_identity_base = os_info_old_value(OS_INFO_IDENTITY_BASE);
 	for_each_physmem_range(idx, &oldmem_type, &start, &end) {
 		phdr->p_type = PT_LOAD;
 		phdr->p_vaddr = old_identity_base + start;
@@ -522,6 +521,11 @@ static void loads_init(Elf64_Phdr *phdr)
 	}
 }
 
+static bool os_info_has_vm(void)
+{
+	return os_info_old_value(OS_INFO_KASLR_OFFSET);
+}
+
 /*
  * Prepare PT_LOAD type program header for kernel image region
  */
@@ -566,7 +570,7 @@ static void *notes_init(Elf64_Phdr *phdr, void *ptr, u64 notes_offset)
 	return ptr;
 }
 
-static size_t get_elfcorehdr_size(int mem_chunk_cnt)
+static size_t get_elfcorehdr_size(int phdr_count)
 {
 	size_t size;
 
@@ -581,10 +585,8 @@ static size_t get_elfcorehdr_size(int mem_chunk_cnt)
 	size += nt_vmcoreinfo_size();
 	/* nt_final */
 	size += sizeof(Elf64_Nhdr);
-	/* PT_LOAD type program header for kernel text region */
-	size += sizeof(Elf64_Phdr);
 	/* PT_LOADS */
-	size += mem_chunk_cnt * sizeof(Elf64_Phdr);
+	size += phdr_count * sizeof(Elf64_Phdr);
 
 	return size;
 }
@@ -595,8 +597,8 @@ static size_t get_elfcorehdr_size(int mem_chunk_cnt)
 int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
 {
 	Elf64_Phdr *phdr_notes, *phdr_loads, *phdr_text;
+	int mem_chunk_cnt, phdr_text_cnt;
 	size_t alloc_size;
-	int mem_chunk_cnt;
 	void *ptr, *hdr;
 	u64 hdr_off;
 
@@ -615,12 +617,14 @@ int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
 	}
 
 	mem_chunk_cnt = get_mem_chunk_cnt();
+	phdr_text_cnt = os_info_has_vm() ? 1 : 0;
 
-	alloc_size = get_elfcorehdr_size(mem_chunk_cnt);
+	alloc_size = get_elfcorehdr_size(mem_chunk_cnt + phdr_text_cnt);
 
 	hdr = kzalloc(alloc_size, GFP_KERNEL);
 
-	/* Without elfcorehdr /proc/vmcore cannot be created. Thus creating
+	/*
+	 * Without elfcorehdr /proc/vmcore cannot be created. Thus creating
 	 * a dump with this crash kernel will fail. Panic now to allow other
 	 * dump mechanisms to take over.
 	 */
@@ -628,21 +632,23 @@ int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
 		panic("s390 kdump allocating elfcorehdr failed");
 
 	/* Init elf header */
-	ptr = ehdr_init(hdr, mem_chunk_cnt);
+	phdr_notes = ehdr_init(hdr, mem_chunk_cnt + phdr_text_cnt);
 	/* Init program headers */
-	phdr_notes = ptr;
-	ptr = PTR_ADD(ptr, sizeof(Elf64_Phdr));
-	phdr_text = ptr;
-	ptr = PTR_ADD(ptr, sizeof(Elf64_Phdr));
-	phdr_loads = ptr;
-	ptr = PTR_ADD(ptr, sizeof(Elf64_Phdr) * mem_chunk_cnt);
+	if (phdr_text_cnt) {
+		phdr_text = phdr_notes + 1;
+		phdr_loads = phdr_text + 1;
+	} else {
+		phdr_loads = phdr_notes + 1;
+	}
+	ptr = PTR_ADD(phdr_loads, sizeof(Elf64_Phdr) * mem_chunk_cnt);
 	/* Init notes */
 	hdr_off = PTR_DIFF(ptr, hdr);
 	ptr = notes_init(phdr_notes, ptr, ((unsigned long) hdr) + hdr_off);
 	/* Init kernel text program header */
+	if (phdr_text_cnt)
 		text_init(phdr_text);
 	/* Init loads */
-	loads_init(phdr_loads);
+	loads_init(phdr_loads, phdr_text_cnt);
 	/* Finalize program headers */
 	hdr_off = PTR_DIFF(ptr, hdr);
 	*addr = (unsigned long long) hdr;

tools/testing/selftests/kvm/Makefile

@@ -183,6 +183,7 @@ TEST_GEN_PROGS_s390x += s390x/sync_regs_test
 TEST_GEN_PROGS_s390x += s390x/tprot
 TEST_GEN_PROGS_s390x += s390x/cmma_test
 TEST_GEN_PROGS_s390x += s390x/debug_test
+TEST_GEN_PROGS_s390x += s390x/shared_zeropage_test
 TEST_GEN_PROGS_s390x += demand_paging_test
 TEST_GEN_PROGS_s390x += dirty_log_test
 TEST_GEN_PROGS_s390x += guest_print_test

tools/testing/selftests/kvm/s390x/shared_zeropage_test.c

@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Test shared zeropage handling (with/without storage keys)
+ *
+ * Copyright (C) 2024, Red Hat, Inc.
+ */
+#include <sys/mman.h>
+
+#include <linux/fs.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "kselftest.h"
+#include "ucall_common.h"
+
+static void set_storage_key(void *addr, uint8_t skey)
+{
+	asm volatile("sske %0,%1" : : "d" (skey), "a" (addr));
+}
+
+static void guest_code(void)
+{
+	/* Issue some storage key instruction. */
+	set_storage_key((void *)0, 0x98);
+	GUEST_DONE();
+}
+
+/*
+ * Returns 1 if the shared zeropage is mapped, 0 if something else is mapped.
+ * Returns < 0 on error or if nothing is mapped.
+ */
+static int maps_shared_zeropage(int pagemap_fd, void *addr)
+{
+	struct page_region region;
+	struct pm_scan_arg arg = {
+		.start = (uintptr_t)addr,
+		.end = (uintptr_t)addr + 4096,
+		.vec = (uintptr_t)&region,
+		.vec_len = 1,
+		.size = sizeof(struct pm_scan_arg),
+		.category_mask = PAGE_IS_PFNZERO,
+		.category_anyof_mask = PAGE_IS_PRESENT,
+		.return_mask = PAGE_IS_PFNZERO,
+	};
+	return ioctl(pagemap_fd, PAGEMAP_SCAN, &arg);
+}
+
+int main(int argc, char *argv[])
+{
+	char *mem, *page0, *page1, *page2, tmp;
+	const size_t pagesize = getpagesize();
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	struct ucall uc;
+	int pagemap_fd;
+
+	ksft_print_header();
+	ksft_set_plan(3);
+
+	/*
+	 * We'll use memory that is not mapped into the VM for simplicity.
+	 * Shared zeropages are enabled/disabled per-process.
+	 */
+	mem = mmap(0, 3 * pagesize, PROT_READ, MAP_PRIVATE | MAP_ANON, -1, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap() failed");
+
+	/* Disable THP. Ignore errors on older kernels. */
+	madvise(mem, 3 * pagesize, MADV_NOHUGEPAGE);
+
+	page0 = mem;
+	page1 = page0 + pagesize;
+	page2 = page1 + pagesize;
+
+	/* Can we even detect shared zeropages? */
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	TEST_REQUIRE(pagemap_fd >= 0);
+
+	tmp = *page0;
+	asm volatile("" : "+r" (tmp));
+	TEST_REQUIRE(maps_shared_zeropage(pagemap_fd, page0) == 1);
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+
+	/* Verify that we get the shared zeropage after VM creation. */
+	tmp = *page1;
+	asm volatile("" : "+r" (tmp));
+	ksft_test_result(maps_shared_zeropage(pagemap_fd, page1) == 1,
+			 "Shared zeropages should be enabled\n");
+
+	/*
+	 * Let our VM execute a storage key instruction that should
+	 * unshare all shared zeropages.
+	 */
+	vcpu_run(vcpu);
+	get_ucall(vcpu, &uc);
+	TEST_ASSERT_EQ(uc.cmd, UCALL_DONE);
+
+	/* Verify that we don't have a shared zeropage anymore. */
+	ksft_test_result(!maps_shared_zeropage(pagemap_fd, page1),
+			 "Shared zeropage should be gone\n");
+
+	/* Verify that we don't get any new shared zeropages. */
+	tmp = *page2;
+	asm volatile("" : "+r" (tmp));
+	ksft_test_result(!maps_shared_zeropage(pagemap_fd, page2),
+			 "Shared zeropages should be disabled\n");
+
+	kvm_vm_free(vm);
+
+	ksft_finished();
+}