linux-kernel - Re: [PATCH Part1 RFC v2 13/20] x86/sev: Register GHCB memory when SEV-SNP is active

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Date:   Wed, 26 May 2021 11:57:49 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, jroedel@...e.de, thomas.lendacky@....com,
        pbonzini@...hat.com, mingo@...hat.com, dave.hansen@...el.com,
        rientjes@...gle.com, seanjc@...gle.com, peterz@...radead.org,
        hpa@...or.com, tony.luck@...el.com
Subject: Re: [PATCH Part1 RFC v2 13/20] x86/sev: Register GHCB memory when
 SEV-SNP is active

On Tue, May 25, 2021 at 09:47:24AM -0500, Brijesh Singh wrote:
> Maybe I should have said, its not applicable in the decompressed path.

Aha, ok. How's that, ontop of yours:

---
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 07b9529d7d95..c9dd98b9dcdf 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -208,7 +208,7 @@ static bool early_setup_sev_es(void)
 
 	/* SEV-SNP guest requires the GHCB GPA must be registered */
 	if (sev_snp_enabled())
-		snp_register_ghcb(__pa(&boot_ghcb_page));
+		snp_register_ghcb_early(__pa(&boot_ghcb_page));
 
 	return true;
 }
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 37a23c524f8c..7200f44d6b6b 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -81,7 +81,7 @@ static bool ghcb_get_hv_features(void)
 	return true;
 }
 
-static void snp_register_ghcb(unsigned long paddr)
+static void snp_register_ghcb_early(unsigned long paddr)
 {
 	unsigned long pfn = paddr >> PAGE_SHIFT;
 	u64 val;
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 5544557d9fb6..144c20479cae 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -108,7 +108,18 @@ DEFINE_STATIC_KEY_FALSE(sev_es_enable_key);
 void do_early_exception(struct pt_regs *regs, int trapnr);
 
 /* Defined in sev-shared.c */
-static void snp_register_ghcb(unsigned long paddr);
+static void snp_register_ghcb_early(unsigned long paddr);
+
+static void snp_register_ghcb(struct sev_es_runtime_data *data,
+			      unsigned long paddr)
+{
+	if (data->snp_ghcb_registered)
+		return;
+
+	snp_register_ghcb_early(paddr);
+
+	data->snp_ghcb_registered = true;
+}
 
 static void __init setup_vc_stacks(int cpu)
 {
@@ -239,10 +250,8 @@ static __always_inline struct ghcb *sev_es_get_ghcb(struct ghcb_state *state)
 	}
 
 	/* SEV-SNP guest requires that GHCB must be registered before using it. */
-	if (sev_snp_active() && !data->snp_ghcb_registered) {
-		snp_register_ghcb(__pa(ghcb));
-		data->snp_ghcb_registered = true;
-	}
+	if (sev_snp_active())
+		snp_register_ghcb(data, __pa(ghcb));
 
 	return ghcb;
 }
@@ -681,7 +690,7 @@ static bool __init sev_es_setup_ghcb(void)
 
 	/* SEV-SNP guest requires that GHCB GPA must be registered */
 	if (sev_snp_active())
-		snp_register_ghcb(__pa(&boot_ghcb_page));
+		snp_register_ghcb_early(__pa(&boot_ghcb_page));
 
 	return true;
 }

-- 
Regards/Gruss,
    Boris.

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