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, 140 insertions, 0 deletions

diff --git a/drivers/firmware/sysfb_simplefb.c b/drivers/firmware/sysfb_simplefb.c
new file mode 100644
index 000000000..71f542e37
--- /dev/null
+++ b/drivers/firmware/sysfb_simplefb.c
@@ -0,0 +1,140 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Generic System Framebuffers
+ * Copyright (c) 2012-2013 David Herrmann <dh.herrmann@gmail.com>
+ */
+
+/*
+ * simple-framebuffer probing
+ * Try to convert "screen_info" into a "simple-framebuffer" compatible mode.
+ * If the mode is incompatible, we return "false" and let the caller create
+ * legacy nodes instead.
+ */
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/platform_data/simplefb.h>
+#include <linux/platform_device.h>
+#include <linux/screen_info.h>
+#include <linux/sysfb.h>
+
+static const char simplefb_resname[] = "BOOTFB";
+static const struct simplefb_format formats[] = SIMPLEFB_FORMATS;
+
+/* try parsing screen_info into a simple-framebuffer mode struct */
+__init bool sysfb_parse_mode(const struct screen_info *si,
+			     struct simplefb_platform_data *mode)
+{
+	__u8 type;
+	u32 bits_per_pixel;
+	unsigned int i;
+
+	type = si->orig_video_isVGA;
+	if (type != VIDEO_TYPE_VLFB && type != VIDEO_TYPE_EFI)
+		return false;
+
+	bits_per_pixel = __screen_info_lfb_bits_per_pixel(si);
+
+	for (i = 0; i < ARRAY_SIZE(formats); ++i) {
+		const struct simplefb_format *f = &formats[i];
+
+		if (f->transp.length)
+			continue; /* transparent formats are unsupported by VESA/EFI */
+
+		if (bits_per_pixel == f->bits_per_pixel &&
+		    si->red_size == f->red.length &&
+		    si->red_pos == f->red.offset &&
+		    si->green_size == f->green.length &&
+		    si->green_pos == f->green.offset &&
+		    si->blue_size == f->blue.length &&
+		    si->blue_pos == f->blue.offset) {
+			mode->format = f->name;
+			mode->width = si->lfb_width;
+			mode->height = si->lfb_height;
+			mode->stride = si->lfb_linelength;
+			return true;
+		}
+	}
+
+	return false;
+}
+
+__init struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
+						     const struct simplefb_platform_data *mode,
+						     struct device *parent)
+{
+	struct platform_device *pd;
+	struct resource res;
+	u64 base, size;
+	u32 length;
+	int ret;
+
+	/*
+	 * If the 64BIT_BASE capability is set, ext_lfb_base will contain the
+	 * upper half of the base address. Assemble the address, then make sure
+	 * it is valid and we can actually access it.
+	 */
+	base = si->lfb_base;
+	if (si->capabilities & VIDEO_CAPABILITY_64BIT_BASE)
+		base |= (u64)si->ext_lfb_base << 32;
+	if (!base || (u64)(resource_size_t)base != base) {
+		printk(KERN_DEBUG "sysfb: inaccessible VRAM base\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	/*
+	 * Don't use lfb_size as IORESOURCE size, since it may contain the
+	 * entire VMEM, and thus require huge mappings. Use just the part we
+	 * need, that is, the part where the framebuffer is located. But verify
+	 * that it does not exceed the advertised VMEM.
+	 * Note that in case of VBE, the lfb_size is shifted by 16 bits for
+	 * historical reasons.
+	 */
+	size = si->lfb_size;
+	if (si->orig_video_isVGA == VIDEO_TYPE_VLFB)
+		size <<= 16;
+	length = mode->height * mode->stride;
+	if (length > size) {
+		printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
+		return ERR_PTR(-EINVAL);
+	}
+	length = PAGE_ALIGN(length);
+
+	/* setup IORESOURCE_MEM as framebuffer memory */
+	memset(&res, 0, sizeof(res));
+	res.flags = IORESOURCE_MEM;
+	res.name = simplefb_resname;
+	res.start = base;
+	res.end = res.start + length - 1;
+	if (res.end <= res.start)
+		return ERR_PTR(-EINVAL);
+
+	pd = platform_device_alloc("simple-framebuffer", 0);
+	if (!pd)
+		return ERR_PTR(-ENOMEM);
+
+	pd->dev.parent = parent;
+
+	sysfb_set_efifb_fwnode(si, pd);
+
+	ret = platform_device_add_resources(pd, &res, 1);
+	if (ret)
+		goto err_put_device;
+
+	ret = platform_device_add_data(pd, mode, sizeof(*mode));
+	if (ret)
+		goto err_put_device;
+
+	ret = platform_device_add(pd);
+	if (ret)
+		goto err_put_device;
+
+	return pd;
+
+err_put_device:
+	platform_device_put(pd);
+
+	return ERR_PTR(ret);
+}