Re: [PATCH] KVM: SVM: Mark SEV launch secret pages as dirty.

[Paolo Bonzini]

On 19/09/20 06:55, Sean Christopherson wrote:
> Side topic, while I love the comment (I do, honestly) regarding in-place
> encryption, this is the fourth? instance of the same 4-line comment (6 lines
> if you count the /* and */.  Maybe it's time to do something like
> 
>       /* LAUNCH_SECRET does in-place encryption, see sev_clflush_pages(). */
> 
> and then have the main comment in sev_clflush_pages().  With the addition of
> X86_FEATURE_SME_COHERENT, there's even a fantastic location for the comment:

Two of the three instances are a bit different though.  What about this
which at least shortens the comment to 2 fewer lines:

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index bb0e89c79a04..7b11546e65ba 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 before LAUNCH_UPDATE encrypts pages in place, in case the cache
+        * contains the data that was written unencrypted.
         */
        sev_clflush_pages(inpages, npages);
 
@@ -805,10 +803,8 @@ 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 before DBG_{DE,EN}CRYPT reads or modifies the pages, 
flush the
+                * destination too in case the cache contains its current data.
                 */
                sev_clflush_pages(src_p, 1);
                sev_clflush_pages(dst_p, 1);
@@ -870,10 +866,8 @@ 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 before LAUNCH_SECRET encrypts pages in place, in case the cache
+        * contains the data that was written unencrypted.
         */
        sev_clflush_pages(pages, n);