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, 148 insertions, 0 deletions

diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
new file mode 100644
index 000000000..f1c04d7cf
--- /dev/null
+++ b/drivers/firmware/efi/memmap.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Common EFI memory map functions.
+ */
+
+#define pr_fmt(fmt) "efi: " fmt
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/efi.h>
+#include <linux/io.h>
+#include <linux/memblock.h>
+#include <linux/slab.h>
+
+#include <asm/early_ioremap.h>
+#include <asm/efi.h>
+
+/**
+ * __efi_memmap_init - Common code for mapping the EFI memory map
+ * @data: EFI memory map data
+ *
+ * This function takes care of figuring out which function to use to
+ * map the EFI memory map in efi.memmap based on how far into the boot
+ * we are.
+ *
+ * During bootup EFI_MEMMAP_LATE in data->flags should be clear since we
+ * only have access to the early_memremap*() functions as the vmalloc
+ * space isn't setup.  Once the kernel is fully booted we can fallback
+ * to the more robust memremap*() API.
+ *
+ * Returns: zero on success, a negative error code on failure.
+ */
+int __init __efi_memmap_init(struct efi_memory_map_data *data)
+{
+	struct efi_memory_map map;
+	phys_addr_t phys_map;
+
+	phys_map = data->phys_map;
+
+	if (data->flags & EFI_MEMMAP_LATE)
+		map.map = memremap(phys_map, data->size, MEMREMAP_WB);
+	else
+		map.map = early_memremap(phys_map, data->size);
+
+	if (!map.map) {
+		pr_err("Could not map the memory map! phys_map=%pa, size=0x%lx\n",
+			&phys_map, data->size);
+		return -ENOMEM;
+	}
+
+	map.phys_map = data->phys_map;
+	map.nr_map = data->size / data->desc_size;
+	map.map_end = map.map + data->size;
+
+	map.desc_version = data->desc_version;
+	map.desc_size = data->desc_size;
+	map.flags = data->flags;
+
+	set_bit(EFI_MEMMAP, &efi.flags);
+
+	efi.memmap = map;
+
+	return 0;
+}
+
+/**
+ * efi_memmap_init_early - Map the EFI memory map data structure
+ * @data: EFI memory map data
+ *
+ * Use early_memremap() to map the passed in EFI memory map and assign
+ * it to efi.memmap.
+ *
+ * Returns: zero on success, a negative error code on failure.
+ */
+int __init efi_memmap_init_early(struct efi_memory_map_data *data)
+{
+	/* Cannot go backwards */
+	WARN_ON(efi.memmap.flags & EFI_MEMMAP_LATE);
+
+	data->flags = 0;
+	return __efi_memmap_init(data);
+}
+
+void __init efi_memmap_unmap(void)
+{
+	if (!efi_enabled(EFI_MEMMAP))
+		return;
+
+	if (!(efi.memmap.flags & EFI_MEMMAP_LATE)) {
+		unsigned long size;
+
+		size = efi.memmap.desc_size * efi.memmap.nr_map;
+		early_memunmap(efi.memmap.map, size);
+	} else {
+		memunmap(efi.memmap.map);
+	}
+
+	efi.memmap.map = NULL;
+	clear_bit(EFI_MEMMAP, &efi.flags);
+}
+
+/**
+ * efi_memmap_init_late - Map efi.memmap with memremap()
+ * @addr: Physical address of the new EFI memory map
+ * @size: Size in bytes of the new EFI memory map
+ *
+ * Setup a mapping of the EFI memory map using ioremap_cache(). This
+ * function should only be called once the vmalloc space has been
+ * setup and is therefore not suitable for calling during early EFI
+ * initialise, e.g. in efi_init(). Additionally, it expects
+ * efi_memmap_init_early() to have already been called.
+ *
+ * The reason there are two EFI memmap initialisation
+ * (efi_memmap_init_early() and this late version) is because the
+ * early EFI memmap should be explicitly unmapped once EFI
+ * initialisation is complete as the fixmap space used to map the EFI
+ * memmap (via early_memremap()) is a scarce resource.
+ *
+ * This late mapping is intended to persist for the duration of
+ * runtime so that things like efi_mem_desc_lookup() and
+ * efi_mem_attributes() always work.
+ *
+ * Returns: zero on success, a negative error code on failure.
+ */
+int __init efi_memmap_init_late(phys_addr_t addr, unsigned long size)
+{
+	struct efi_memory_map_data data = {
+		.phys_map = addr,
+		.size = size,
+		.flags = EFI_MEMMAP_LATE,
+	};
+
+	/* Did we forget to unmap the early EFI memmap? */
+	WARN_ON(efi.memmap.map);
+
+	/* Were we already called? */
+	WARN_ON(efi.memmap.flags & EFI_MEMMAP_LATE);
+
+	/*
+	 * It makes no sense to allow callers to register different
+	 * values for the following fields. Copy them out of the
+	 * existing early EFI memmap.
+	 */
+	data.desc_version = efi.memmap.desc_version;
+	data.desc_size = efi.memmap.desc_size;
+
+	return __efi_memmap_init(&data);
+}