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, 133 insertions, 0 deletions

diff --git a/drivers/firmware/efi/fdtparams.c b/drivers/firmware/efi/fdtparams.c
new file mode 100644
index 000000000..b815d2a75
--- /dev/null
+++ b/drivers/firmware/efi/fdtparams.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#define pr_fmt(fmt) "efi: " fmt
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/efi.h>
+#include <linux/libfdt.h>
+#include <linux/of_fdt.h>
+
+#include <linux/unaligned.h>
+
+enum {
+	SYSTAB,
+	MMBASE,
+	MMSIZE,
+	DCSIZE,
+	DCVERS,
+
+	PARAMCOUNT
+};
+
+static __initconst const char name[][22] = {
+	[SYSTAB] = "System Table         ",
+	[MMBASE] = "MemMap Address       ",
+	[MMSIZE] = "MemMap Size          ",
+	[DCSIZE] = "MemMap Desc. Size    ",
+	[DCVERS] = "MemMap Desc. Version ",
+};
+
+static __initconst const struct {
+	const char	path[17];
+	u8		paravirt;
+	const char	params[PARAMCOUNT][26];
+} dt_params[] = {
+	{
+#ifdef CONFIG_XEN    //  <-------17------>
+		.path = "/hypervisor/uefi",
+		.paravirt = 1,
+		.params = {
+			[SYSTAB] = "xen,uefi-system-table",
+			[MMBASE] = "xen,uefi-mmap-start",
+			[MMSIZE] = "xen,uefi-mmap-size",
+			[DCSIZE] = "xen,uefi-mmap-desc-size",
+			[DCVERS] = "xen,uefi-mmap-desc-ver",
+		}
+	}, {
+#endif
+		.path = "/chosen",
+		.params = {	//  <-----------26----------->
+			[SYSTAB] = "linux,uefi-system-table",
+			[MMBASE] = "linux,uefi-mmap-start",
+			[MMSIZE] = "linux,uefi-mmap-size",
+			[DCSIZE] = "linux,uefi-mmap-desc-size",
+			[DCVERS] = "linux,uefi-mmap-desc-ver",
+		}
+	}
+};
+
+static int __init efi_get_fdt_prop(const void *fdt, int node, const char *pname,
+				   const char *rname, void *var, int size)
+{
+	const void *prop;
+	int len;
+	u64 val;
+
+	prop = fdt_getprop(fdt, node, pname, &len);
+	if (!prop)
+		return 1;
+
+	val = (len == 4) ? (u64)be32_to_cpup(prop) : get_unaligned_be64(prop);
+
+	if (size == 8)
+		*(u64 *)var = val;
+	else
+		*(u32 *)var = (val < U32_MAX) ? val : U32_MAX; // saturate
+
+	if (efi_enabled(EFI_DBG))
+		pr_info("  %s: 0x%0*llx\n", rname, size * 2, val);
+
+	return 0;
+}
+
+u64 __init efi_get_fdt_params(struct efi_memory_map_data *mm)
+{
+	const void *fdt = initial_boot_params;
+	unsigned long systab;
+	int i, j, node;
+	struct {
+		void	*var;
+		int	size;
+	} target[] = {
+		[SYSTAB] = { &systab,		sizeof(systab) },
+		[MMBASE] = { &mm->phys_map,	sizeof(mm->phys_map) },
+		[MMSIZE] = { &mm->size,		sizeof(mm->size) },
+		[DCSIZE] = { &mm->desc_size,	sizeof(mm->desc_size) },
+		[DCVERS] = { &mm->desc_version,	sizeof(mm->desc_version) },
+	};
+
+	BUILD_BUG_ON(ARRAY_SIZE(target) != ARRAY_SIZE(name));
+	BUILD_BUG_ON(ARRAY_SIZE(target) != ARRAY_SIZE(dt_params[0].params));
+
+	if (!fdt)
+		return 0;
+
+	for (i = 0; i < ARRAY_SIZE(dt_params); i++) {
+		node = fdt_path_offset(fdt, dt_params[i].path);
+		if (node < 0)
+			continue;
+
+		if (efi_enabled(EFI_DBG))
+			pr_info("Getting UEFI parameters from %s in DT:\n",
+				dt_params[i].path);
+
+		for (j = 0; j < ARRAY_SIZE(target); j++) {
+			const char *pname = dt_params[i].params[j];
+
+			if (!efi_get_fdt_prop(fdt, node, pname, name[j],
+					      target[j].var, target[j].size))
+				continue;
+			if (!j)
+				goto notfound;
+			pr_err("Can't find property '%s' in DT!\n", pname);
+			return 0;
+		}
+		if (dt_params[i].paravirt)
+			set_bit(EFI_PARAVIRT, &efi.flags);
+		return systab;
+	}
+notfound:
+	pr_info("UEFI not found.\n");
+	return 0;
+}