2020-09-23 17:36:05

by Paolo Bonzini

Subject: [PATCH] KVM: SEV: shorten comments around sev_clflush_pages

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 <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
---
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

2020-09-23 18:10:49

by Sean Christopherson

Subject: Re: [PATCH] KVM: SEV: shorten comments around sev_clflush_pages

On Wed, Sep 23, 2020 at 01:34:01PM -0400, Paolo Bonzini wrote:
> 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 <[email protected]>
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---

Reviewed-by: Sean Christopherson <[email protected]>