KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 178 insertions, 0 deletions

diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
new file mode 100644
index 000000000..d6b5c27a0
--- /dev/null
+++ b/arch/arc/mm/init.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/memblock.h>
+#ifdef CONFIG_BLK_DEV_INITRD
+#include <linux/initrd.h>
+#endif
+#include <linux/of_fdt.h>
+#include <linux/swap.h>
+#include <linux/module.h>
+#include <linux/highmem.h>
+#include <asm/page.h>
+#include <asm/sections.h>
+#include <asm/setup.h>
+#include <asm/arcregs.h>
+
+pgd_t swapper_pg_dir[PTRS_PER_PGD] __aligned(PAGE_SIZE);
+
+static const unsigned long low_mem_start = CONFIG_LINUX_RAM_BASE;
+static unsigned long low_mem_sz;
+
+#ifdef CONFIG_HIGHMEM
+static unsigned long min_high_pfn, max_high_pfn;
+static phys_addr_t high_mem_start;
+static phys_addr_t high_mem_sz;
+unsigned long arch_pfn_offset;
+EXPORT_SYMBOL(arch_pfn_offset);
+#endif
+
+long __init arc_get_mem_sz(void)
+{
+	return low_mem_sz;
+}
+
+/* User can over-ride above with "mem=nnn[KkMm]" in cmdline */
+static int __init setup_mem_sz(char *str)
+{
+	low_mem_sz = memparse(str, NULL) & PAGE_MASK;
+
+	/* early console might not be setup yet - it will show up later */
+	pr_info("\"mem=%s\": mem sz set to %ldM\n", str, TO_MB(low_mem_sz));
+
+	return 0;
+}
+early_param("mem", setup_mem_sz);
+
+void __init early_init_dt_add_memory_arch(u64 base, u64 size)
+{
+	int in_use = 0;
+
+	if (!low_mem_sz) {
+		if (base != low_mem_start)
+			panic("CONFIG_LINUX_RAM_BASE != DT memory { }");
+
+		low_mem_sz = size;
+		in_use = 1;
+		memblock_add_node(base, size, 0, MEMBLOCK_NONE);
+	} else {
+#ifdef CONFIG_HIGHMEM
+		high_mem_start = base;
+		high_mem_sz = size;
+		in_use = 1;
+		memblock_add_node(base, size, 1, MEMBLOCK_NONE);
+		memblock_reserve(base, size);
+#endif
+	}
+
+	pr_info("Memory @ %llx [%lldM] %s\n",
+		base, TO_MB(size), !in_use ? "Not used":"");
+}
+
+void __init arch_zone_limits_init(unsigned long *max_zone_pfn)
+{
+	/*----------------- node/zones setup --------------------------*/
+	max_zone_pfn[ZONE_NORMAL] = max_low_pfn;
+
+#ifdef CONFIG_HIGHMEM
+	/*
+	 * max_high_pfn should be ok here for both HIGHMEM and HIGHMEM+PAE.
+	 * For HIGHMEM without PAE max_high_pfn should be less than
+	 * min_low_pfn to guarantee that these two regions don't overlap.
+	 * For PAE case highmem is greater than lowmem, so it is natural
+	 * to use max_high_pfn.
+	 *
+	 * In both cases, holes should be handled by pfn_valid().
+	 */
+	max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
+#endif
+}
+
+/*
+ * First memory setup routine called from setup_arch()
+ * 1. setup swapper's mm @init_mm
+ * 2. Count the pages we have and setup bootmem allocator
+ * 3. zone setup
+ */
+void __init setup_arch_memory(void)
+{
+	setup_initial_init_mm(_text, _etext, _edata, _end);
+
+	/* first page of system - kernel .vector starts here */
+	min_low_pfn = virt_to_pfn((void *)CONFIG_LINUX_RAM_BASE);
+
+	/* Last usable page of low mem */
+	max_low_pfn = max_pfn = PFN_DOWN(low_mem_start + low_mem_sz);
+
+	/*------------- bootmem allocator setup -----------------------*/
+
+	/*
+	 * seed the bootmem allocator after any DT memory node parsing or
+	 * "mem=xxx" cmdline overrides have potentially updated @arc_mem_sz
+	 *
+	 * Only low mem is added, otherwise we have crashes when allocating
+	 * mem_map[] itself. NO_BOOTMEM allocates mem_map[] at the end of
+	 * avail memory, ending in highmem with a > 32-bit address. However
+	 * it then tries to memset it with a truncaed 32-bit handle, causing
+	 * the crash
+	 */
+
+	memblock_reserve(CONFIG_LINUX_LINK_BASE,
+			 __pa(_end) - CONFIG_LINUX_LINK_BASE);
+
+#ifdef CONFIG_BLK_DEV_INITRD
+	if (phys_initrd_size) {
+		memblock_reserve(phys_initrd_start, phys_initrd_size);
+		initrd_start = (unsigned long)__va(phys_initrd_start);
+		initrd_end = initrd_start + phys_initrd_size;
+	}
+#endif
+
+	early_init_fdt_reserve_self();
+	early_init_fdt_scan_reserved_mem();
+
+	memblock_dump_all();
+
+#ifdef CONFIG_HIGHMEM
+	/*
+	 * On ARC (w/o PAE) HIGHMEM addresses are actually smaller (0 based)
+	 * than addresses in normal aka low memory (0x8000_0000 based).
+	 * Even with PAE, the huge peripheral space hole would waste a lot of
+	 * mem with single contiguous mem_map[].
+	 * Thus when HIGHMEM on ARC is enabled the memory map corresponding
+	 * to the hole is freed and ARC specific version of pfn_valid()
+	 * handles the hole in the memory map.
+	 */
+
+	min_high_pfn = PFN_DOWN(high_mem_start);
+	max_high_pfn = PFN_DOWN(high_mem_start + high_mem_sz);
+
+	arch_pfn_offset = min(min_low_pfn, min_high_pfn);
+	kmap_init();
+#endif /* CONFIG_HIGHMEM */
+}
+
+void __init arch_mm_preinit(void)
+{
+#ifdef CONFIG_HIGHMEM
+	memblock_phys_free(high_mem_start, high_mem_sz);
+#endif
+
+	BUILD_BUG_ON((PTRS_PER_PGD * sizeof(pgd_t)) > PAGE_SIZE);
+	BUILD_BUG_ON((PTRS_PER_PUD * sizeof(pud_t)) > PAGE_SIZE);
+	BUILD_BUG_ON((PTRS_PER_PMD * sizeof(pmd_t)) > PAGE_SIZE);
+	BUILD_BUG_ON((PTRS_PER_PTE * sizeof(pte_t)) > PAGE_SIZE);
+}
+
+#ifdef CONFIG_HIGHMEM
+int pfn_valid(unsigned long pfn)
+{
+	return (pfn >= min_high_pfn && pfn <= max_high_pfn) ||
+		(pfn >= min_low_pfn && pfn <= max_low_pfn);
+}
+EXPORT_SYMBOL(pfn_valid);
+#endif