From: Stefan Fritsch <sf@sfritsch.de>
Subject: SEV-ES: Relocate ghcb in C, not assembler
To: tech@openbsd.org
Date: Fri, 21 Nov 2025 14:54:50 +0100

Hi,

ghcb_vaddr is not used in locore0.S, no need to do the relocation in 
assembler.

While there, clarify a comment. When I read about vmm(4) I always think 
about openbsd being the hypervisor. But this piece of code is about 
openbsd being the guest.

ok?

Cheers,
Stefan

diff --git a/sys/arch/amd64/amd64/locore0.S b/sys/arch/amd64/amd64/locore0.S
index 4533b19df2f..951da60b1d2 100644
--- a/sys/arch/amd64/amd64/locore0.S
+++ b/sys/arch/amd64/amd64/locore0.S
@@ -804,15 +804,6 @@ longmode_hi:
 	addq	%rsi,%rdx
 	movq	%rdx,atdevbase(%rip)
 
-	/* Relocate GHCB. */
-	movq	cpu_sev_guestmode(%rip),%rax
-	testq	$SEV_STAT_ES_ENABLED,%rax
-	jz	.Lnoghcbreloc
-	movq	$(PROC0_GHCB_OFF+KERNBASE),%rdx
-	addq	%rsi,%rdx
-	movq	%rdx,ghcb_vaddr(%rip)
-
-.Lnoghcbreloc:
 	/* Record start of symbols */
 	movq	$__kernel_bss_end, ssym(%rip)
 
diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index adb0fc11898..5770f17503a 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -1354,8 +1354,9 @@ cpu_init_early_vctrap(paddr_t addr)
 	    GSEL(GCODE_SEL, SEL_KPL));
 	cpu_init_idt();
 
-	/* Tell vmm(4) about our GHCB. */
+	/* Tell the hypervisor about our GHCB. */
 	ghcb_paddr = addr;
+	ghcb_vaddr = addr + KERNBASE;
 	memset((void *)ghcb_vaddr, 0, 2 * PAGE_SIZE);
 	wrmsr(MSR_SEV_GHCB, ghcb_paddr);
 }
-- 
2.39.5