x86/sev: Expose sev_es_ghcb_hv_call() for use by HyperV

Hyper-V needs to issue the GHCB HV call in order to read/write MSRs in
Isolation VMs. For that, expose sev_es_ghcb_hv_call().

The Hyper-V Isolation VMs are unenlightened guests and run a paravisor
at VMPL0 for communicating. GHCB pages are being allocated and set up
by that paravisor. Linux gets the GHCB page's physical address via
MSR_AMD64_SEV_ES_GHCB from the paravisor and should not change it.

Add a @set_ghcb_msr parameter to sev_es_ghcb_hv_call() to control
whether the function should set the GHCB's address prior to the call or
not and export that function for use by HyperV.

  [ bp: - Massage commit message
        - add a struct ghcb forward declaration to fix randconfig builds. ]

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20211025122116.264793-6-ltykernel@gmail.com

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index fa5cd05..ec060c4 100644 (file)
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -53,6 +53,7 @@ static inline u64 lower_bits(u64 val, unsigned int bits)
 
 struct real_mode_header;
 enum stack_type;
+struct ghcb;
 
 /* Early IDT entry points for #VC handler */
 extern void vc_no_ghcb(void);
@@ -81,6 +82,11 @@ static __always_inline void sev_es_nmi_complete(void)
                __sev_es_nmi_complete();
 }
 extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
+extern enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
+                                         bool set_ghcb_msr,
+                                         struct es_em_ctxt *ctxt,
+                                         u64 exit_code, u64 exit_info_1,
+                                         u64 exit_info_2);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 4579c38..0aacd60 100644 (file)
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -125,10 +125,9 @@ static enum es_result verify_exception_info(struct ghcb *ghcb, struct es_em_ctxt
        return ES_VMM_ERROR;
 }
 
-static 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 sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
+                                  struct es_em_ctxt *ctxt, u64 exit_code,
+                                  u64 exit_info_1, u64 exit_info_2)
 {
        /* Fill in protocol and format specifiers */
        ghcb->protocol_version = GHCB_PROTOCOL_MAX;
@@ -138,7 +137,14 @@ 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 unenlightened guests use a paravisor for communicating and
+        * GHCB pages are being allocated and set up by that paravisor. Linux
+        * should not change the GHCB page's physical address.
+        */
+       if (set_ghcb_msr)
+               sev_es_wr_ghcb_msr(__pa(ghcb));
+
        VMGEXIT();
 
        return verify_exception_info(ghcb, ctxt);
@@ -418,7 +424,7 @@ static enum es_result vc_handle_ioio(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
                 */
                sw_scratch = __pa(ghcb) + offsetof(struct ghcb, shared_buffer);
                ghcb_set_sw_scratch(ghcb, sw_scratch);
-               ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_IOIO,
+               ret = sev_es_ghcb_hv_call(ghcb, true, ctxt, SVM_EXIT_IOIO,
                                          exit_info_1, exit_info_2);
                if (ret != ES_OK)
                        return ret;
@@ -460,7 +466,8 @@ static enum es_result vc_handle_ioio(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 
                ghcb_set_rax(ghcb, rax);
 
-               ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_IOIO, exit_info_1, 0);
+               ret = sev_es_ghcb_hv_call(ghcb, true, ctxt,
+                                         SVM_EXIT_IOIO, exit_info_1, 0);
                if (ret != ES_OK)
                        return ret;
 
@@ -491,7 +498,7 @@ static enum es_result vc_handle_cpuid(struct ghcb *ghcb,
                /* xgetbv will cause #GP - use reset value for xcr0 */
                ghcb_set_xcr0(ghcb, 1);
 
-       ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_CPUID, 0, 0);
+       ret = sev_es_ghcb_hv_call(ghcb, true, ctxt, SVM_EXIT_CPUID, 0, 0);
        if (ret != ES_OK)
                return ret;
 
@@ -516,7 +523,7 @@ static enum es_result vc_handle_rdtsc(struct ghcb *ghcb,
        bool rdtscp = (exit_code == SVM_EXIT_RDTSCP);
        enum es_result ret;
 
-       ret = sev_es_ghcb_hv_call(ghcb, ctxt, exit_code, 0, 0);
+       ret = sev_es_ghcb_hv_call(ghcb, true, ctxt, exit_code, 0, 0);
        if (ret != ES_OK)
                return ret;
 

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 2de1f36..113d3ae 100644 (file)
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -648,7 +648,8 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
                ghcb_set_rdx(ghcb, regs->dx);
        }
 
-       ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_MSR, exit_info_1, 0);
+       ret = sev_es_ghcb_hv_call(ghcb, true, ctxt, SVM_EXIT_MSR,
+                                 exit_info_1, 0);
 
        if ((ret == ES_OK) && (!exit_info_1)) {
                regs->ax = ghcb->save.rax;
@@ -867,7 +868,7 @@ static enum es_result vc_do_mmio(struct ghcb *ghcb, struct es_em_ctxt *ctxt,
 
        ghcb_set_sw_scratch(ghcb, ghcb_pa + offsetof(struct ghcb, shared_buffer));
 
-       return sev_es_ghcb_hv_call(ghcb, ctxt, exit_code, exit_info_1, exit_info_2);
+       return sev_es_ghcb_hv_call(ghcb, true, ctxt, exit_code, exit_info_1, exit_info_2);
 }
 
 static enum es_result vc_handle_mmio_twobyte_ops(struct ghcb *ghcb,
@@ -1117,7 +1118,7 @@ static enum es_result vc_handle_dr7_write(struct ghcb *ghcb,
 
        /* Using a value of 0 for ExitInfo1 means RAX holds the value */
        ghcb_set_rax(ghcb, val);
-       ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_WRITE_DR7, 0, 0);
+       ret = sev_es_ghcb_hv_call(ghcb, true, ctxt, SVM_EXIT_WRITE_DR7, 0, 0);
        if (ret != ES_OK)
                return ret;
 
@@ -1147,7 +1148,7 @@ static enum es_result vc_handle_dr7_read(struct ghcb *ghcb,
 static enum es_result vc_handle_wbinvd(struct ghcb *ghcb,
                                       struct es_em_ctxt *ctxt)
 {
-       return sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_WBINVD, 0, 0);
+       return sev_es_ghcb_hv_call(ghcb, true, ctxt, SVM_EXIT_WBINVD, 0, 0);
 }
 
 static enum es_result vc_handle_rdpmc(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
@@ -1156,7 +1157,7 @@ static enum es_result vc_handle_rdpmc(struct ghcb *ghcb, struct es_em_ctxt *ctxt
 
        ghcb_set_rcx(ghcb, ctxt->regs->cx);
 
-       ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_RDPMC, 0, 0);
+       ret = sev_es_ghcb_hv_call(ghcb, true, ctxt, SVM_EXIT_RDPMC, 0, 0);
        if (ret != ES_OK)
                return ret;
 
@@ -1197,7 +1198,7 @@ static enum es_result vc_handle_vmmcall(struct ghcb *ghcb,
        if (x86_platform.hyper.sev_es_hcall_prepare)
                x86_platform.hyper.sev_es_hcall_prepare(ghcb, ctxt->regs);
 
-       ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_VMMCALL, 0, 0);
+       ret = sev_es_ghcb_hv_call(ghcb, true, ctxt, SVM_EXIT_VMMCALL, 0, 0);
        if (ret != ES_OK)
                return ret;