On 8/2/2021 8:28 PM, Joerg Roedel wrote:

On Wed, Jul 28, 2021 at 10:52:20AM -0400, Tianyu Lan wrote:

quoted

+void hv_ghcb_msr_write(u64 msr, u64 value)
+{
+	union hv_ghcb *hv_ghcb;
+	void **ghcb_base;
+	unsigned long flags;
+
+	if (!ms_hyperv.ghcb_base)
+		return;
+
+	WARN_ON(in_nmi());
+
+	local_irq_save(flags);
+	ghcb_base = (void **)this_cpu_ptr(ms_hyperv.ghcb_base);
+	hv_ghcb = (union hv_ghcb *)*ghcb_base;
+	if (!hv_ghcb) {
+		local_irq_restore(flags);
+		return;
+	}
+
+	memset(hv_ghcb, 0x00, HV_HYP_PAGE_SIZE);

Do you really need to zero out the whole 4k? The validation bitmap
should be enough, there are no secrets on the page anyway.
Same in hv_ghcb_msr_read().

OK. Thanks for suggestion. I will have a try.

quoted

+enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
+				   struct es_em_ctxt *ctxt,
+				   u64 exit_code, u64 exit_info_1,
+				   u64 exit_info_2)
  {
  	enum es_result ret;
  

@@ -109,7 +109,16 @@ static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
  	ghcb_set_sw_exit_info_1(ghcb, exit_info_1);
  	ghcb_set_sw_exit_info_2(ghcb, exit_info_2);
  
-	sev_es_wr_ghcb_msr(__pa(ghcb));
+	/*
+	 * Hyper-V runs paravisor with SEV. Ghcb page is allocated by
+	 * paravisor and not needs to be updated in the Linux guest.
+	 * Otherwise, the ghcb page's PA reported by paravisor is above
+	 * VTOM. Hyper-V use this function with NULL for ctxt point and
+	 * skip setting ghcb page in such case.
+	 */
+	if (ctxt)
+		sev_es_wr_ghcb_msr(__pa(ghcb));

No, do not make this function work with ctxt==NULL. Instead, factor out
a helper function which contains what Hyper-V needs and use that in
sev_es_ghcb_hv_call() and Hyper-V code.

OK. Will update.

quoted

+union hv_ghcb {
+	struct ghcb ghcb;
+} __packed __aligned(PAGE_SIZE);

I am curious what this will end up being good for.

Hyper-V introduces a specific hypercall request in GHCB page and use 
same union in the Linux Hyper-V code to read/write MSR and call the new 
hypercall request.
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