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, 190 insertions, 0 deletions

diff --git a/arch/alpha/boot/main.c b/arch/alpha/boot/main.c
new file mode 100644
index 000000000..22a1cb026
--- /dev/null
+++ b/arch/alpha/boot/main.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * arch/alpha/boot/main.c
+ *
+ * Copyright (C) 1994, 1995 Linus Torvalds
+ *
+ * This file is the bootloader for the Linux/AXP kernel
+ */
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <generated/utsrelease.h>
+#include <linux/mm.h>
+
+#include <asm/console.h>
+#include <asm/hwrpb.h>
+
+#include <linux/stdarg.h>
+
+#include "ksize.h"
+
+extern unsigned long switch_to_osf_pal(unsigned long nr,
+	struct pcb_struct * pcb_va, struct pcb_struct * pcb_pa,
+	unsigned long *vptb);
+struct hwrpb_struct *hwrpb = INIT_HWRPB;
+static struct pcb_struct pcb_va[1];
+
+/*
+ * Find a physical address of a virtual object..
+ *
+ * This is easy using the virtual page table address.
+ */
+
+static inline void *
+find_pa(unsigned long *vptb, void *ptr)
+{
+	unsigned long address = (unsigned long) ptr;
+	unsigned long result;
+
+	result = vptb[address >> 13];
+	result >>= 32;
+	result <<= 13;
+	result |= address & 0x1fff;
+	return (void *) result;
+}	
+
+/*
+ * This function moves into OSF/1 pal-code, and has a temporary
+ * PCB for that. The kernel proper should replace this PCB with
+ * the real one as soon as possible.
+ *
+ * The page table muckery in here depends on the fact that the boot
+ * code has the L1 page table identity-map itself in the second PTE
+ * in the L1 page table. Thus the L1-page is virtually addressable
+ * itself (through three levels) at virtual address 0x200802000.
+ */
+
+#define VPTB	((unsigned long *) 0x200000000)
+#define L1	((unsigned long *) 0x200802000)
+
+void
+pal_init(void)
+{
+	unsigned long i, rev;
+	struct percpu_struct * percpu;
+	struct pcb_struct * pcb_pa;
+
+	/* Create the dummy PCB.  */
+	pcb_va->ksp = 0;
+	pcb_va->usp = 0;
+	pcb_va->ptbr = L1[1] >> 32;
+	pcb_va->asn = 0;
+	pcb_va->pcc = 0;
+	pcb_va->unique = 0;
+	pcb_va->flags = 1;
+	pcb_va->res1 = 0;
+	pcb_va->res2 = 0;
+	pcb_pa = find_pa(VPTB, pcb_va);
+
+	/*
+	 * a0 = 2 (OSF)
+	 * a1 = return address, but we give the asm the vaddr of the PCB
+	 * a2 = physical addr of PCB
+	 * a3 = new virtual page table pointer
+	 * a4 = KSP (but the asm sets it)
+	 */
+	srm_printk("Switching to OSF PAL-code .. ");
+
+	i = switch_to_osf_pal(2, pcb_va, pcb_pa, VPTB);
+	if (i) {
+		srm_printk("failed, code %ld\n", i);
+		__halt();
+	}
+
+	percpu = (struct percpu_struct *)
+		(INIT_HWRPB->processor_offset + (unsigned long) INIT_HWRPB);
+	rev = percpu->pal_revision = percpu->palcode_avail[2];
+
+	srm_printk("Ok (rev %lx)\n", rev);
+
+	tbia(); /* do it directly in case we are SMP */
+}
+
+static inline long openboot(void)
+{
+	char bootdev[256];
+	long result;
+
+	result = callback_getenv(ENV_BOOTED_DEV, bootdev, 255);
+	if (result < 0)
+		return result;
+	return callback_open(bootdev, result & 255);
+}
+
+static inline long close(long dev)
+{
+	return callback_close(dev);
+}
+
+static inline long load(long dev, unsigned long addr, unsigned long count)
+{
+	char bootfile[256];
+	extern char _end;
+	long result, boot_size = &_end - (char *) BOOT_ADDR;
+
+	result = callback_getenv(ENV_BOOTED_FILE, bootfile, 255);
+	if (result < 0)
+		return result;
+	result &= 255;
+	bootfile[result] = '\0';
+	if (result)
+		srm_printk("Boot file specification (%s) not implemented\n",
+		       bootfile);
+	return callback_read(dev, count, (void *)addr, boot_size/512 + 1);
+}
+
+/*
+ * Start the kernel.
+ */
+static void runkernel(void)
+{
+	__asm__ __volatile__(
+		"bis %1,%1,$30\n\t"
+		"bis %0,%0,$26\n\t"
+		"ret ($26)"
+		: /* no outputs: it doesn't even return */
+		: "r" (START_ADDR),
+		  "r" (PAGE_SIZE + INIT_STACK));
+}
+
+void start_kernel(void)
+{
+	long i;
+	long dev;
+	int nbytes;
+	char envval[256];
+
+	srm_printk("Linux/AXP bootloader for Linux " UTS_RELEASE "\n");
+	if (INIT_HWRPB->pagesize != 8192) {
+		srm_printk("Expected 8kB pages, got %ldkB\n", INIT_HWRPB->pagesize >> 10);
+		return;
+	}
+	pal_init();
+	dev = openboot();
+	if (dev < 0) {
+		srm_printk("Unable to open boot device: %016lx\n", dev);
+		return;
+	}
+	dev &= 0xffffffff;
+	srm_printk("Loading vmlinux ...");
+	i = load(dev, START_ADDR, KERNEL_SIZE);
+	close(dev);
+	if (i != KERNEL_SIZE) {
+		srm_printk("Failed (%lx)\n", i);
+		return;
+	}
+
+	nbytes = callback_getenv(ENV_BOOTED_OSFLAGS, envval, sizeof(envval));
+	if (nbytes < 0) {
+		nbytes = 0;
+	}
+	envval[nbytes] = '\0';
+	strcpy((char*)ZERO_PGE, envval);
+
+	srm_printk(" Ok\nNow booting the kernel\n");
+	runkernel();
+	for (i = 0 ; i < 0x100000000 ; i++)
+		/* nothing */;
+	__halt();
+}