Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Received-SPF: Pass (protection.outlook.com: domain of amd.com designates
 165.204.84.17 as permitted sender) receiver=protection.outlook.com;
 client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C
From:   Tom Lendacky <thomas.lendacky@amd.com>
To:     <linux-kernel@vger.kernel.org>, <x86@kernel.org>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Michael Roth <michael.roth@amd.com>,
        Joerg Roedel <jroedel@suse.de>,
        Dionna Glaze <dionnaglaze@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: [PATCH v7 3/6] x86/sev: Allow for use of the early boot GHCB for PSC requests
Date:   Tue, 4 Apr 2023 12:23:03 -0500
Message-ID: <79ae3cce825217f150560a1ab6fc1fd947b406c4.1680628986.git.thomas.lendacky@amd.com>
In-Reply-To: <cover.1680628986.git.thomas.lendacky@amd.com>
References: <20230330114956.20342-1-kirill.shutemov@linux.intel.com> <cover.1680628986.git.thomas.lendacky@amd.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Apr 2023 17:23:44.5943
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 849db2aa-54fa-4b9e-092e-08db353157d9
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com]
X-MS-Exchange-CrossTenant-AuthSource: DS1PEPF0000E641.namprd02.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW5PR12MB5600
X-Spam-Status: No, score=0.8 required=5.0 tests=DKIM_SIGNED,DKIM_VALID,
        DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,RCVD_IN_DNSWL_NONE,
        RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE autolearn=no
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Using a GHCB for a page stage change (as opposed to the MSR protocol)
allows for multiple pages to be processed in a single request. In prep
for early PSC requests in support of unaccepted memory, update the
invocation of vmgexit_psc() to be able to use the early boot GHCB and not
just the per-CPU GHCB structure.

In order to use the proper GHCB (early boot vs per-CPU), set a flag that
indicates when the per-CPU GHCBs are available and registered. For APs,
the per-CPU GHCBs are created before they are started and registered upon
startup, so this flag can be used globally for the BSP and APs instead of
creating a per-CPU flag. This will allow for a significant reduction in
the number of MSR protocol page state change requests when accepting
memory.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/kernel/sev.c | 61 +++++++++++++++++++++++++++----------------
 1 file changed, 38 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a3d76eb344d6..1717bc4558f7 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -117,7 +117,19 @@ static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
 
 struct sev_config {
 	__u64 debug		: 1,
-	      __reserved	: 63;
+
+	      /*
+	       * A flag used by __set_pages_state() that indicates when the
+	       * per-CPU GHCB has been created and registered and thus can be
+	       * used by the BSP instead of the early boot GHCB.
+	       *
+	       * For APs, the per-CPU GHCB is created before they are started
+	       * and registered upon startup, so this flag can be used globally
+	       * for the BSP and APs.
+	       */
+	      ghcbs_initialized	: 1,
+
+	      __reserved	: 62;
 };
 
 static struct sev_config sev_cfg __read_mostly;
@@ -660,7 +672,7 @@ static void pvalidate_pages(unsigned long vaddr, unsigned long npages, bool vali
 	}
 }
 
-static void __init early_set_pages_state(unsigned long paddr, unsigned long npages, enum psc_op op)
+static void early_set_pages_state(unsigned long paddr, unsigned long npages, enum psc_op op)
 {
 	unsigned long paddr_end;
 	u64 val;
@@ -754,26 +766,13 @@ void __init snp_prep_memory(unsigned long paddr, unsigned int sz, enum psc_op op
 		WARN(1, "invalid memory op %d\n", op);
 }
 
-static int vmgexit_psc(struct snp_psc_desc *desc)
+static int vmgexit_psc(struct ghcb *ghcb, struct snp_psc_desc *desc)
 {
 	int cur_entry, end_entry, ret = 0;
 	struct snp_psc_desc *data;
-	struct ghcb_state state;
 	struct es_em_ctxt ctxt;
-	unsigned long flags;
-	struct ghcb *ghcb;
 
-	/*
-	 * __sev_get_ghcb() needs to run with IRQs disabled because it is using
-	 * a per-CPU GHCB.
-	 */
-	local_irq_save(flags);
-
-	ghcb = __sev_get_ghcb(&state);
-	if (!ghcb) {
-		ret = 1;
-		goto out_unlock;
-	}
+	vc_ghcb_invalidate(ghcb);
 
 	/* Copy the input desc into GHCB shared buffer */
 	data = (struct snp_psc_desc *)ghcb->shared_buffer;
@@ -830,20 +829,18 @@ static int vmgexit_psc(struct snp_psc_desc *desc)
 	}
 
 out:
-	__sev_put_ghcb(&state);
-
-out_unlock:
-	local_irq_restore(flags);
-
 	return ret;
 }
 
 static void __set_pages_state(struct snp_psc_desc *data, unsigned long vaddr,
 			      unsigned long vaddr_end, int op)
 {
+	struct ghcb_state state;
 	struct psc_hdr *hdr;
 	struct psc_entry *e;
+	unsigned long flags;
 	unsigned long pfn;
+	struct ghcb *ghcb;
 	int i;
 
 	hdr = &data->hdr;
@@ -873,8 +870,20 @@ static void __set_pages_state(struct snp_psc_desc *data, unsigned long vaddr,
 		i++;
 	}
 
-	if (vmgexit_psc(data))
+	local_irq_save(flags);
+
+	if (sev_cfg.ghcbs_initialized)
+		ghcb = __sev_get_ghcb(&state);
+	else
+		ghcb = boot_ghcb;
+
+	if (!ghcb || vmgexit_psc(ghcb, data))
 		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PSC);
+
+	if (sev_cfg.ghcbs_initialized)
+		__sev_put_ghcb(&state);
+
+	local_irq_restore(flags);
 }
 
 static void set_pages_state(unsigned long vaddr, unsigned long npages, int op)
@@ -882,6 +891,10 @@ static void set_pages_state(unsigned long vaddr, unsigned long npages, int op)
 	unsigned long vaddr_end, next_vaddr;
 	struct snp_psc_desc desc;
 
+	/* Use the MSR protocol when a GHCB is not available. */
+	if (!boot_ghcb)
+		return early_set_pages_state(__pa(vaddr), npages, op);
+
 	vaddr = vaddr & PAGE_MASK;
 	vaddr_end = vaddr + (npages << PAGE_SHIFT);
 
@@ -1259,6 +1272,8 @@ void setup_ghcb(void)
 		if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
 			snp_register_per_cpu_ghcb();
 
+		sev_cfg.ghcbs_initialized = true;
+
 		return;
 	}
 
-- 
2.40.0