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, 275 insertions, 0 deletions

diff --git a/drivers/firmware/efi/earlycon.c b/drivers/firmware/efi/earlycon.c
new file mode 100644
index 000000000..3d060d599
--- /dev/null
+++ b/drivers/firmware/efi/earlycon.c
@@ -0,0 +1,275 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2013 Intel Corporation; author Matt Fleming
+ */
+
+#include <linux/console.h>
+#include <linux/efi.h>
+#include <linux/font.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/serial_core.h>
+#include <linux/sysfb.h>
+#include <linux/string.h>
+
+#include <asm/early_ioremap.h>
+
+static const struct console *earlycon_console __initdata;
+static const struct font_desc *font;
+static u16 cur_line_y, max_line_y;
+static u32 efi_x_array[1024];
+static u32 efi_x, efi_y;
+static u64 fb_base;
+static bool fb_wb;
+static void *efi_fb;
+
+/*
+ * EFI earlycon needs to use early_memremap() to map the framebuffer.
+ * But early_memremap() is not usable for 'earlycon=efifb keep_bootcon',
+ * memremap() should be used instead. memremap() will be available after
+ * paging_init() which is earlier than initcall callbacks. Thus adding this
+ * early initcall function early_efi_map_fb() to map the whole EFI framebuffer.
+ */
+static int __init efi_earlycon_remap_fb(void)
+{
+	const struct screen_info *si = &sysfb_primary_display.screen;
+
+	/* bail if there is no bootconsole or it was unregistered already */
+	if (!earlycon_console || !console_is_registered(earlycon_console))
+		return 0;
+
+	efi_fb = memremap(fb_base, si->lfb_size, fb_wb ? MEMREMAP_WB : MEMREMAP_WC);
+
+	return efi_fb ? 0 : -ENOMEM;
+}
+early_initcall(efi_earlycon_remap_fb);
+
+static int __init efi_earlycon_unmap_fb(void)
+{
+	/* unmap the bootconsole fb unless keep_bootcon left it registered */
+	if (efi_fb && !console_is_registered(earlycon_console))
+		memunmap(efi_fb);
+	return 0;
+}
+late_initcall(efi_earlycon_unmap_fb);
+
+static __ref void *efi_earlycon_map(unsigned long start, unsigned long len)
+{
+	pgprot_t fb_prot;
+
+	if (efi_fb)
+		return efi_fb + start;
+
+	fb_prot = fb_wb ? PAGE_KERNEL : pgprot_writecombine(PAGE_KERNEL);
+	return early_memremap_prot(fb_base + start, len, pgprot_val(fb_prot));
+}
+
+static __ref void efi_earlycon_unmap(void *addr, unsigned long len)
+{
+	if (efi_fb)
+		return;
+
+	early_memunmap(addr, len);
+}
+
+static void efi_earlycon_clear_scanline(unsigned int y, const struct screen_info *si)
+{
+	unsigned long *dst;
+	u16 len;
+
+	len = si->lfb_linelength;
+	dst = efi_earlycon_map(y*len, len);
+	if (!dst)
+		return;
+
+	memset(dst, 0, len);
+	efi_earlycon_unmap(dst, len);
+}
+
+static void efi_earlycon_scroll_up(const struct screen_info *si)
+{
+	unsigned long *dst, *src;
+	u16 maxlen = 0;
+	u16 len;
+	u32 i, height;
+
+	/* Find the cached maximum x coordinate */
+	for (i = 0; i < max_line_y; i++) {
+		if (efi_x_array[i] > maxlen)
+			maxlen = efi_x_array[i];
+	}
+	maxlen *= 4;
+
+	len = si->lfb_linelength;
+	height = si->lfb_height;
+
+	for (i = 0; i < height - font->height; i++) {
+		dst = efi_earlycon_map(i*len, len);
+		if (!dst)
+			return;
+
+		src = efi_earlycon_map((i + font->height) * len, len);
+		if (!src) {
+			efi_earlycon_unmap(dst, len);
+			return;
+		}
+
+		memmove(dst, src, maxlen);
+
+		efi_earlycon_unmap(src, len);
+		efi_earlycon_unmap(dst, len);
+	}
+}
+
+static void efi_earlycon_write_char(u32 *dst, unsigned char c, unsigned int h,
+				    const struct screen_info *si)
+{
+	const u32 color_black = 0x00000000;
+	const u32 color_white = 0x00ffffff;
+	const u8 *src;
+	int m, n, bytes;
+	u8 x;
+
+	bytes = BITS_TO_BYTES(font->width);
+	src = font->data + c * font->height * bytes + h * bytes;
+
+	for (m = 0; m < font->width; m++) {
+		n = m % 8;
+		x = *(src + m / 8);
+		if ((x >> (7 - n)) & 1)
+			*dst = color_white;
+		else
+			*dst = color_black;
+		dst++;
+	}
+}
+
+static void
+efi_earlycon_write(struct console *con, const char *str, unsigned int num)
+{
+	const struct screen_info *si = &sysfb_primary_display.screen;
+	u32 cur_efi_x = efi_x;
+	unsigned int len;
+	const char *s;
+	void *dst;
+
+	len = si->lfb_linelength;
+
+	while (num) {
+		unsigned int linemax = (si->lfb_width - efi_x) / font->width;
+		unsigned int h, count;
+
+		count = strnchrnul(str, num, '\n') - str;
+		if (count > linemax)
+			count = linemax;
+
+		for (h = 0; h < font->height; h++) {
+			unsigned int n, x;
+
+			dst = efi_earlycon_map((efi_y + h) * len, len);
+			if (!dst)
+				return;
+
+			s = str;
+			n = count;
+			x = efi_x;
+
+			while (n-- > 0) {
+				efi_earlycon_write_char(dst + x * 4, *s, h, si);
+				x += font->width;
+				s++;
+			}
+
+			efi_earlycon_unmap(dst, len);
+		}
+
+		num -= count;
+		efi_x += count * font->width;
+		str += count;
+
+		if (num > 0 && *s == '\n') {
+			cur_efi_x = efi_x;
+			efi_x = 0;
+			efi_y += font->height;
+			str++;
+			num--;
+		}
+
+		if (efi_x + font->width > si->lfb_width) {
+			cur_efi_x = efi_x;
+			efi_x = 0;
+			efi_y += font->height;
+		}
+
+		if (efi_y + font->height > si->lfb_height) {
+			u32 i;
+
+			efi_x_array[cur_line_y] = cur_efi_x;
+			cur_line_y = (cur_line_y + 1) % max_line_y;
+
+			efi_y -= font->height;
+			efi_earlycon_scroll_up(si);
+
+			for (i = 0; i < font->height; i++)
+				efi_earlycon_clear_scanline(efi_y + i, si);
+		}
+	}
+}
+
+static bool __initdata fb_probed;
+
+void __init efi_earlycon_reprobe(void)
+{
+	if (fb_probed)
+		setup_earlycon("efifb");
+}
+
+static int __init efi_earlycon_setup(struct earlycon_device *device,
+				     const char *opt)
+{
+	const struct screen_info *si = &sysfb_primary_display.screen;
+	u16 xres, yres;
+	u32 i;
+
+	fb_wb = opt && !strcmp(opt, "ram");
+
+	if (si->orig_video_isVGA != VIDEO_TYPE_EFI) {
+		fb_probed = true;
+		return -ENODEV;
+	}
+
+	fb_base = si->lfb_base;
+	if (si->capabilities & VIDEO_CAPABILITY_64BIT_BASE)
+		fb_base |= (u64)si->ext_lfb_base << 32;
+
+	xres = si->lfb_width;
+	yres = si->lfb_height;
+
+	/*
+	 * efi_earlycon_write_char() implicitly assumes a framebuffer with
+	 * 32 bits per pixel.
+	 */
+	if (si->lfb_depth != 32)
+		return -ENODEV;
+
+	font = get_default_font(xres, yres, NULL, NULL);
+	if (!font)
+		return -ENODEV;
+
+	/* Fill the cache with maximum possible value of x coordinate */
+	memset32(efi_x_array, rounddown(xres, font->width), ARRAY_SIZE(efi_x_array));
+	efi_y = rounddown(yres, font->height);
+
+	/* Make sure we have cache for the x coordinate for the full screen */
+	max_line_y = efi_y / font->height + 1;
+	cur_line_y = 0;
+
+	efi_y -= font->height;
+	for (i = 0; i < (yres - efi_y) / font->height; i++)
+		efi_earlycon_scroll_up(si);
+
+	device->con->write = efi_earlycon_write;
+	earlycon_console = device->con;
+	return 0;
+}
+EARLYCON_DECLARE(efifb, efi_earlycon_setup);