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, 177 insertions, 0 deletions

diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
new file mode 100644
index 000000000..5018ac03b
--- /dev/null
+++ b/arch/arm64/lib/mte.S
@@ -0,0 +1,177 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 ARM Ltd.
+ */
+#include <linux/linkage.h>
+
+#include <asm/asm-uaccess.h>
+#include <asm/assembler.h>
+#include <asm/mte.h>
+#include <asm/page.h>
+#include <asm/sysreg.h>
+
+	.arch	armv8.5-a+memtag
+
+/*
+ * multitag_transfer_size - set \reg to the block size that is accessed by the
+ * LDGM/STGM instructions.
+ */
+	.macro	multitag_transfer_size, reg, tmp
+	mrs_s	\reg, SYS_GMID_EL1
+	ubfx	\reg, \reg, #GMID_EL1_BS_SHIFT, #GMID_EL1_BS_WIDTH
+	mov	\tmp, #4
+	lsl	\reg, \tmp, \reg
+	.endm
+
+/*
+ * Clear the tags in a page
+ *   x0 - address of the page to be cleared
+ */
+SYM_FUNC_START(mte_clear_page_tags)
+	multitag_transfer_size x1, x2
+1:	stgm	xzr, [x0]
+	add	x0, x0, x1
+	tst	x0, #(PAGE_SIZE - 1)
+	b.ne	1b
+	ret
+SYM_FUNC_END(mte_clear_page_tags)
+
+/*
+ * Zero the page and tags at the same time
+ *
+ * Parameters:
+ *	x0 - address to the beginning of the page
+ */
+SYM_FUNC_START(mte_zero_clear_page_tags)
+	and	x0, x0, #(1 << MTE_TAG_SHIFT) - 1	// clear the tag
+	mrs	x1, dczid_el0
+	tbnz	x1, #4, 2f	// Branch if DC GZVA is prohibited
+	and	w1, w1, #0xf
+	mov	x2, #4
+	lsl	x1, x2, x1
+
+1:	dc	gzva, x0
+	add	x0, x0, x1
+	tst	x0, #(PAGE_SIZE - 1)
+	b.ne	1b
+	ret
+
+2:	stz2g	x0, [x0], #(MTE_GRANULE_SIZE * 2)
+	tst	x0, #(PAGE_SIZE - 1)
+	b.ne	2b
+	ret
+SYM_FUNC_END(mte_zero_clear_page_tags)
+
+/*
+ * Copy the tags from the source page to the destination one
+ *   x0 - address of the destination page
+ *   x1 - address of the source page
+ */
+SYM_FUNC_START(mte_copy_page_tags)
+	mov	x2, x0
+	mov	x3, x1
+	multitag_transfer_size x5, x6
+1:	ldgm	x4, [x3]
+	stgm	x4, [x2]
+	add	x2, x2, x5
+	add	x3, x3, x5
+	tst	x2, #(PAGE_SIZE - 1)
+	b.ne	1b
+	ret
+SYM_FUNC_END(mte_copy_page_tags)
+
+/*
+ * Read tags from a user buffer (one tag per byte) and set the corresponding
+ * tags at the given kernel address. Used by PTRACE_POKEMTETAGS.
+ *   x0 - kernel address (to)
+ *   x1 - user buffer (from)
+ *   x2 - number of tags/bytes (n)
+ * Returns:
+ *   x0 - number of tags read/set
+ */
+SYM_FUNC_START(mte_copy_tags_from_user)
+	mov	x3, x1
+	cbz	x2, 2f
+1:
+USER(2f, ldtrb	w4, [x1])
+	lsl	x4, x4, #MTE_TAG_SHIFT
+	stg	x4, [x0], #MTE_GRANULE_SIZE
+	add	x1, x1, #1
+	subs	x2, x2, #1
+	b.ne	1b
+
+	// exception handling and function return
+2:	sub	x0, x1, x3		// update the number of tags set
+	ret
+SYM_FUNC_END(mte_copy_tags_from_user)
+
+/*
+ * Get the tags from a kernel address range and write the tag values to the
+ * given user buffer (one tag per byte). Used by PTRACE_PEEKMTETAGS.
+ *   x0 - user buffer (to)
+ *   x1 - kernel address (from)
+ *   x2 - number of tags/bytes (n)
+ * Returns:
+ *   x0 - number of tags read/set
+ */
+SYM_FUNC_START(mte_copy_tags_to_user)
+	mov	x3, x0
+	cbz	x2, 2f
+1:
+	ldg	x4, [x1]
+	ubfx	x4, x4, #MTE_TAG_SHIFT, #MTE_TAG_SIZE
+USER(2f, sttrb	w4, [x0])
+	add	x0, x0, #1
+	add	x1, x1, #MTE_GRANULE_SIZE
+	subs	x2, x2, #1
+	b.ne	1b
+
+	// exception handling and function return
+2:	sub	x0, x0, x3		// update the number of tags copied
+	ret
+SYM_FUNC_END(mte_copy_tags_to_user)
+
+/*
+ * Save the tags in a page
+ *   x0 - page address
+ *   x1 - tag storage, MTE_PAGE_TAG_STORAGE bytes
+ */
+SYM_FUNC_START(mte_save_page_tags)
+	multitag_transfer_size x7, x5
+1:
+	mov	x2, #0
+2:
+	ldgm	x5, [x0]
+	orr	x2, x2, x5
+	add	x0, x0, x7
+	tst	x0, #0xFF		// 16 tag values fit in a register,
+	b.ne	2b			// which is 16*16=256 bytes
+
+	str	x2, [x1], #8
+
+	tst	x0, #(PAGE_SIZE - 1)
+	b.ne	1b
+
+	ret
+SYM_FUNC_END(mte_save_page_tags)
+
+/*
+ * Restore the tags in a page
+ *   x0 - page address
+ *   x1 - tag storage, MTE_PAGE_TAG_STORAGE bytes
+ */
+SYM_FUNC_START(mte_restore_page_tags)
+	multitag_transfer_size x7, x5
+1:
+	ldr	x2, [x1], #8
+2:
+	stgm	x2, [x0]
+	add	x0, x0, x7
+	tst	x0, #0xFF
+	b.ne	2b
+
+	tst	x0, #(PAGE_SIZE - 1)
+	b.ne	1b
+
+	ret
+SYM_FUNC_END(mte_restore_page_tags)