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, 82 insertions, 0 deletions

diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c
new file mode 100644
index 000000000..f80a67c09
--- /dev/null
+++ b/arch/mips/lib/uncached.c
@@ -0,0 +1,82 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2005 Thiemo Seufer
+ * Copyright (C) 2005  MIPS Technologies, Inc.	All rights reserved.
+ *	Author: Maciej W. Rozycki <macro@mips.com>
+ */
+
+
+#include <asm/addrspace.h>
+#include <asm/bug.h>
+#include <asm/cacheflush.h>
+
+#ifndef CKSEG2
+#define CKSEG2 CKSSEG
+#endif
+#ifndef TO_PHYS_MASK
+#define TO_PHYS_MASK -1
+#endif
+
+/*
+ * FUNC is executed in one of the uncached segments, depending on its
+ * original address as follows:
+ *
+ * 1. If the original address is in CKSEG0 or CKSEG1, then the uncached
+ *    segment used is CKSEG1.
+ * 2. If the original address is in XKPHYS, then the uncached segment
+ *    used is XKPHYS(2).
+ * 3. Otherwise it's a bug.
+ *
+ * The same remapping is done with the stack pointer.  Stack handling
+ * works because we don't handle stack arguments or more complex return
+ * values, so we can avoid sharing the same stack area between a cached
+ * and the uncached mode.
+ */
+unsigned long run_uncached(void *func)
+{
+	register long ret __asm__("$2");
+	long lfunc = (long)func, ufunc;
+	long usp;
+	long sp;
+
+	__asm__("move %0, $sp" : "=r" (sp));
+
+	if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
+		usp = CKSEG1ADDR(sp);
+#ifdef CONFIG_64BIT
+	else if ((long long)sp >= (long long)PHYS_TO_XKPHYS(0, 0) &&
+		 (long long)sp < (long long)PHYS_TO_XKPHYS(8, 0))
+		usp = PHYS_TO_XKPHYS(K_CALG_UNCACHED,
+				     XKPHYS_TO_PHYS((long long)sp));
+#endif
+	else {
+		BUG();
+		usp = sp;
+	}
+	if (lfunc >= (long)CKSEG0 && lfunc < (long)CKSEG2)
+		ufunc = CKSEG1ADDR(lfunc);
+#ifdef CONFIG_64BIT
+	else if ((long long)lfunc >= (long long)PHYS_TO_XKPHYS(0, 0) &&
+		 (long long)lfunc < (long long)PHYS_TO_XKPHYS(8, 0))
+		ufunc = PHYS_TO_XKPHYS(K_CALG_UNCACHED,
+				       XKPHYS_TO_PHYS((long long)lfunc));
+#endif
+	else {
+		BUG();
+		ufunc = lfunc;
+	}
+
+	__asm__ __volatile__ (
+		"	move	$16, $sp\n"
+		"	move	$sp, %1\n"
+		"	jalr	%2\n"
+		"	move	$sp, $16"
+		: "=r" (ret)
+		: "r" (usp), "r" (ufunc)
+		: "$16", "$31");
+
+	return ret;
+}