Re: [PATCH 05/13] HV: Add Write/Read MSR registers via ghcb page
From: Joerg Roedel <joro@8bytes.org>
Date: 2021-08-02 12:28:49
Also in:
linux-arch, linux-hyperv, linux-iommu, lkml, netdev, xen-devel
On Wed, Jul 28, 2021 at 10:52:20AM -0400, Tianyu Lan wrote:
+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().
quoted hunk ↗ jump to hunk
+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.
+union hv_ghcb {
+ struct ghcb ghcb;
+} __packed __aligned(PAGE_SIZE);I am curious what this will end up being good for.