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, 91 insertions, 0 deletions

diff --git a/arch/arm/lib/io-writesb.S b/arch/arm/lib/io-writesb.S
new file mode 100644
index 000000000..e2ae312f0
--- /dev/null
+++ b/arch/arm/lib/io-writesb.S
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/arch/arm/lib/io-writesb.S
+ *
+ *  Copyright (C) 1995-2000 Russell King
+ */
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+		.macro	outword, rd
+#ifndef __ARMEB__
+		strb	\rd, [r0]
+		mov	\rd, \rd, lsr #8
+		strb	\rd, [r0]
+		mov	\rd, \rd, lsr #8
+		strb	\rd, [r0]
+		mov	\rd, \rd, lsr #8
+		strb	\rd, [r0]
+#else
+		mov	lr, \rd, lsr #24
+		strb	lr, [r0]
+		mov	lr, \rd, lsr #16
+		strb	lr, [r0]
+		mov	lr, \rd, lsr #8
+		strb	lr, [r0]
+		strb	\rd, [r0]
+#endif
+		.endm
+
+.Loutsb_align:	rsb	ip, ip, #4
+		cmp	ip, r2
+		movgt	ip, r2
+		cmp	ip, #2
+		ldrb	r3, [r1], #1
+		strb	r3, [r0]
+		ldrbge	r3, [r1], #1
+		strbge	r3, [r0]
+		ldrbgt	r3, [r1], #1
+		strbgt	r3, [r0]
+		subs	r2, r2, ip
+		bne	.Loutsb_aligned
+
+ENTRY(__raw_writesb)
+		teq	r2, #0		@ do we have to check for the zero len?
+		reteq	lr
+		ands	ip, r1, #3
+		bne	.Loutsb_align
+
+.Loutsb_aligned:
+		stmfd	sp!, {r4, r5, lr}
+
+		subs	r2, r2, #16
+		bmi	.Loutsb_no_16
+
+.Loutsb_16_lp:	ldmia	r1!, {r3, r4, r5, ip}
+		outword	r3
+		outword	r4
+		outword	r5
+		outword	ip
+		subs	r2, r2, #16
+		bpl	.Loutsb_16_lp
+
+		tst	r2, #15
+		ldmfdeq	sp!, {r4, r5, pc}
+
+.Loutsb_no_16:	tst	r2, #8
+		beq	.Loutsb_no_8
+
+		ldmia	r1!, {r3, r4}
+		outword	r3
+		outword	r4
+
+.Loutsb_no_8:	tst	r2, #4
+		beq	.Loutsb_no_4
+
+		ldr	r3, [r1], #4
+		outword	r3
+
+.Loutsb_no_4:	ands	r2, r2, #3
+		ldmfdeq	sp!, {r4, r5, pc}
+
+		cmp	r2, #2
+		ldrb	r3, [r1], #1
+		strb	r3, [r0]
+		ldrbge	r3, [r1], #1
+		strbge	r3, [r0]
+		ldrbgt	r3, [r1]
+		strbgt	r3, [r0]
+
+		ldmfd	sp!, {r4, r5, pc}
+ENDPROC(__raw_writesb)