From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration 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 Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/lib/usercopy.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 arch/x86/lib/usercopy.c (limited to 'arch/x86/lib/usercopy.c') diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c new file mode 100644 index 000000000..24b48af27 --- /dev/null +++ b/arch/x86/lib/usercopy.c @@ -0,0 +1,55 @@ +/* + * User address space access functions. + * + * For licencing details see kernel-base/COPYING + */ + +#include +#include +#include + +#include + +/** + * copy_from_user_nmi - NMI safe copy from user + * @to: Pointer to the destination buffer + * @from: Pointer to a user space address of the current task + * @n: Number of bytes to copy + * + * Returns: The number of not copied bytes. 0 is success, i.e. all bytes copied + * + * Contrary to other copy_from_user() variants this function can be called + * from NMI context. Despite the name it is not restricted to be called + * from NMI context. It is safe to be called from any other context as + * well. It disables pagefaults across the copy which means a fault will + * abort the copy. + * + * For NMI context invocations this relies on the nested NMI work to allow + * atomic faults from the NMI path; the nested NMI paths are careful to + * preserve CR2. + */ +unsigned long +copy_from_user_nmi(void *to, const void __user *from, unsigned long n) +{ + unsigned long ret; + + if (!__access_ok(from, n)) + return n; + + if (!nmi_uaccess_okay()) + return n; + + /* + * Even though this function is typically called from NMI/IRQ context + * disable pagefaults so that its behaviour is consistent even when + * called from other contexts. + */ + pagefault_disable(); + instrument_copy_from_user_before(to, from, n); + ret = raw_copy_from_user(to, from, n); + instrument_copy_from_user_after(to, from, n, ret); + pagefault_enable(); + + return ret; +} +EXPORT_SYMBOL_GPL(copy_from_user_nmi); -- cgit v1.3.1