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, 233 insertions, 0 deletions

diff --git a/arch/alpha/lib/fpreg.c b/arch/alpha/lib/fpreg.c
new file mode 100644
index 000000000..3d3216504
--- /dev/null
+++ b/arch/alpha/lib/fpreg.c
@@ -0,0 +1,233 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * arch/alpha/lib/fpreg.c
+ *
+ * (C) Copyright 1998 Linus Torvalds
+ */
+
+#include <linux/compiler.h>
+#include <linux/export.h>
+#include <linux/preempt.h>
+#include <asm/fpu.h>
+#include <asm/thread_info.h>
+
+#if defined(CONFIG_ALPHA_EV6) || defined(CONFIG_ALPHA_EV67)
+#define STT(reg,val)  asm volatile ("ftoit $f"#reg",%0" : "=r"(val));
+#else
+#define STT(reg,val)  asm volatile ("stt $f"#reg",%0" : "=m"(val));
+#endif
+
+unsigned long
+alpha_read_fp_reg (unsigned long reg)
+{
+	unsigned long val;
+
+	if (unlikely(reg >= 32))
+		return 0;
+	preempt_disable();
+	if (current_thread_info()->status & TS_SAVED_FP)
+		val = current_thread_info()->fp[reg];
+	else switch (reg) {
+	      case  0: STT( 0, val); break;
+	      case  1: STT( 1, val); break;
+	      case  2: STT( 2, val); break;
+	      case  3: STT( 3, val); break;
+	      case  4: STT( 4, val); break;
+	      case  5: STT( 5, val); break;
+	      case  6: STT( 6, val); break;
+	      case  7: STT( 7, val); break;
+	      case  8: STT( 8, val); break;
+	      case  9: STT( 9, val); break;
+	      case 10: STT(10, val); break;
+	      case 11: STT(11, val); break;
+	      case 12: STT(12, val); break;
+	      case 13: STT(13, val); break;
+	      case 14: STT(14, val); break;
+	      case 15: STT(15, val); break;
+	      case 16: STT(16, val); break;
+	      case 17: STT(17, val); break;
+	      case 18: STT(18, val); break;
+	      case 19: STT(19, val); break;
+	      case 20: STT(20, val); break;
+	      case 21: STT(21, val); break;
+	      case 22: STT(22, val); break;
+	      case 23: STT(23, val); break;
+	      case 24: STT(24, val); break;
+	      case 25: STT(25, val); break;
+	      case 26: STT(26, val); break;
+	      case 27: STT(27, val); break;
+	      case 28: STT(28, val); break;
+	      case 29: STT(29, val); break;
+	      case 30: STT(30, val); break;
+	      case 31: STT(31, val); break;
+	}
+	preempt_enable();
+	return val;
+}
+EXPORT_SYMBOL(alpha_read_fp_reg);
+
+#if defined(CONFIG_ALPHA_EV6) || defined(CONFIG_ALPHA_EV67)
+#define LDT(reg,val)  asm volatile ("itoft %0,$f"#reg : : "r"(val));
+#else
+#define LDT(reg,val)  asm volatile ("ldt $f"#reg",%0" : : "m"(val));
+#endif
+
+void
+alpha_write_fp_reg (unsigned long reg, unsigned long val)
+{
+	if (unlikely(reg >= 32))
+		return;
+
+	preempt_disable();
+	if (current_thread_info()->status & TS_SAVED_FP) {
+		current_thread_info()->status |= TS_RESTORE_FP;
+		current_thread_info()->fp[reg] = val;
+	} else switch (reg) {
+	      case  0: LDT( 0, val); break;
+	      case  1: LDT( 1, val); break;
+	      case  2: LDT( 2, val); break;
+	      case  3: LDT( 3, val); break;
+	      case  4: LDT( 4, val); break;
+	      case  5: LDT( 5, val); break;
+	      case  6: LDT( 6, val); break;
+	      case  7: LDT( 7, val); break;
+	      case  8: LDT( 8, val); break;
+	      case  9: LDT( 9, val); break;
+	      case 10: LDT(10, val); break;
+	      case 11: LDT(11, val); break;
+	      case 12: LDT(12, val); break;
+	      case 13: LDT(13, val); break;
+	      case 14: LDT(14, val); break;
+	      case 15: LDT(15, val); break;
+	      case 16: LDT(16, val); break;
+	      case 17: LDT(17, val); break;
+	      case 18: LDT(18, val); break;
+	      case 19: LDT(19, val); break;
+	      case 20: LDT(20, val); break;
+	      case 21: LDT(21, val); break;
+	      case 22: LDT(22, val); break;
+	      case 23: LDT(23, val); break;
+	      case 24: LDT(24, val); break;
+	      case 25: LDT(25, val); break;
+	      case 26: LDT(26, val); break;
+	      case 27: LDT(27, val); break;
+	      case 28: LDT(28, val); break;
+	      case 29: LDT(29, val); break;
+	      case 30: LDT(30, val); break;
+	      case 31: LDT(31, val); break;
+	}
+	preempt_enable();
+}
+EXPORT_SYMBOL(alpha_write_fp_reg);
+
+#if defined(CONFIG_ALPHA_EV6) || defined(CONFIG_ALPHA_EV67)
+#define STS(reg,val)  asm volatile ("ftois $f"#reg",%0" : "=r"(val));
+#else
+#define STS(reg,val)  asm volatile ("sts $f"#reg",%0" : "=m"(val));
+#endif
+
+unsigned long
+alpha_read_fp_reg_s (unsigned long reg)
+{
+	unsigned long val;
+
+	if (unlikely(reg >= 32))
+		return 0;
+
+	preempt_disable();
+	if (current_thread_info()->status & TS_SAVED_FP) {
+		LDT(0, current_thread_info()->fp[reg]);
+		STS(0, val);
+	} else switch (reg) {
+	      case  0: STS( 0, val); break;
+	      case  1: STS( 1, val); break;
+	      case  2: STS( 2, val); break;
+	      case  3: STS( 3, val); break;
+	      case  4: STS( 4, val); break;
+	      case  5: STS( 5, val); break;
+	      case  6: STS( 6, val); break;
+	      case  7: STS( 7, val); break;
+	      case  8: STS( 8, val); break;
+	      case  9: STS( 9, val); break;
+	      case 10: STS(10, val); break;
+	      case 11: STS(11, val); break;
+	      case 12: STS(12, val); break;
+	      case 13: STS(13, val); break;
+	      case 14: STS(14, val); break;
+	      case 15: STS(15, val); break;
+	      case 16: STS(16, val); break;
+	      case 17: STS(17, val); break;
+	      case 18: STS(18, val); break;
+	      case 19: STS(19, val); break;
+	      case 20: STS(20, val); break;
+	      case 21: STS(21, val); break;
+	      case 22: STS(22, val); break;
+	      case 23: STS(23, val); break;
+	      case 24: STS(24, val); break;
+	      case 25: STS(25, val); break;
+	      case 26: STS(26, val); break;
+	      case 27: STS(27, val); break;
+	      case 28: STS(28, val); break;
+	      case 29: STS(29, val); break;
+	      case 30: STS(30, val); break;
+	      case 31: STS(31, val); break;
+	}
+	preempt_enable();
+	return val;
+}
+EXPORT_SYMBOL(alpha_read_fp_reg_s);
+
+#if defined(CONFIG_ALPHA_EV6) || defined(CONFIG_ALPHA_EV67)
+#define LDS(reg,val)  asm volatile ("itofs %0,$f"#reg : : "r"(val));
+#else
+#define LDS(reg,val)  asm volatile ("lds $f"#reg",%0" : : "m"(val));
+#endif
+
+void
+alpha_write_fp_reg_s (unsigned long reg, unsigned long val)
+{
+	if (unlikely(reg >= 32))
+		return;
+
+	preempt_disable();
+	if (current_thread_info()->status & TS_SAVED_FP) {
+		current_thread_info()->status |= TS_RESTORE_FP;
+		LDS(0, val);
+		STT(0, current_thread_info()->fp[reg]);
+	} else switch (reg) {
+	      case  0: LDS( 0, val); break;
+	      case  1: LDS( 1, val); break;
+	      case  2: LDS( 2, val); break;
+	      case  3: LDS( 3, val); break;
+	      case  4: LDS( 4, val); break;
+	      case  5: LDS( 5, val); break;
+	      case  6: LDS( 6, val); break;
+	      case  7: LDS( 7, val); break;
+	      case  8: LDS( 8, val); break;
+	      case  9: LDS( 9, val); break;
+	      case 10: LDS(10, val); break;
+	      case 11: LDS(11, val); break;
+	      case 12: LDS(12, val); break;
+	      case 13: LDS(13, val); break;
+	      case 14: LDS(14, val); break;
+	      case 15: LDS(15, val); break;
+	      case 16: LDS(16, val); break;
+	      case 17: LDS(17, val); break;
+	      case 18: LDS(18, val); break;
+	      case 19: LDS(19, val); break;
+	      case 20: LDS(20, val); break;
+	      case 21: LDS(21, val); break;
+	      case 22: LDS(22, val); break;
+	      case 23: LDS(23, val); break;
+	      case 24: LDS(24, val); break;
+	      case 25: LDS(25, val); break;
+	      case 26: LDS(26, val); break;
+	      case 27: LDS(27, val); break;
+	      case 28: LDS(28, val); break;
+	      case 29: LDS(29, val); break;
+	      case 30: LDS(30, val); break;
+	      case 31: LDS(31, val); break;
+	}
+	preempt_enable();
+}
+EXPORT_SYMBOL(alpha_write_fp_reg_s);