Very similar content is present in four comments in sev.c. Unfortunately
there are small differences that make it harder to place the comment
in sev_clflush_pages itself, but at least we can make it more concise.
Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/svm/sev.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index bb0e89c79a04..65e15c22bd3c 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -446,10 +446,8 @@ static int sev_launch_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
}
/*
- * The LAUNCH_UPDATE command will perform in-place encryption of the
- * memory content (i.e it will write the same memory region with C=1).
- * It's possible that the cache may contain the data with C=0, i.e.,
- * unencrypted so invalidate it first.
+ * Flush (on non-coherent CPUs) before LAUNCH_UPDATE encrypts pages in
+ * place; the cache may contain the data that was written unencrypted.
*/
sev_clflush_pages(inpages, npages);
@@ -805,10 +803,9 @@ static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
}
/*
- * The DBG_{DE,EN}CRYPT commands will perform {dec,en}cryption of the
- * memory content (i.e it will write the same memory region with C=1).
- * It's possible that the cache may contain the data with C=0, i.e.,
- * unencrypted so invalidate it first.
+ * Flush (on non-coherent CPUs) before DBG_{DE,EN}CRYPT read or modify
+ * the pages; flush the destination too so that future accesses do not
+ * see stale data.
*/
sev_clflush_pages(src_p, 1);
sev_clflush_pages(dst_p, 1);
@@ -870,10 +867,8 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
return PTR_ERR(pages);
/*
- * The LAUNCH_SECRET command will perform in-place encryption of the
- * memory content (i.e it will write the same memory region with C=1).
- * It's possible that the cache may contain the data with C=0, i.e.,
- * unencrypted so invalidate it first.
+ * Flush (on non-coherent CPUs) before LAUNCH_SECRET encrypts pages in
+ * place; the cache may contain the data that was written unencrypted.
*/
sev_clflush_pages(pages, n);
--
2.26.2
