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Peter Anvin" , Michael Roth , Joerg Roedel , Andy Lutomirski , Peter Zijlstra Subject: [PATCH v6 2/5] x86/sev: Put PSC struct on the stack in prep for unaccepted memory support Date: Thu, 8 Dec 2022 09:29:10 -0600 Message-ID: X-Mailer: git-send-email 2.38.1 In-Reply-To: References: <20221207014933.8435-1-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB03.amd.com (10.181.40.144) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN8NAM11FT036:EE_|PH7PR12MB6812:EE_ X-MS-Office365-Filtering-Correlation-Id: 1cac1db8-dfbc-4c34-6dc1-08dad93106af X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230022)(4636009)(376002)(396003)(136003)(39860400002)(346002)(451199015)(40470700004)(36840700001)(46966006)(36756003)(81166007)(356005)(86362001)(2906002)(41300700001)(4326008)(70586007)(36860700001)(70206006)(8676002)(8936002)(7416002)(966005)(83380400001)(110136005)(316002)(40460700003)(54906003)(2616005)(478600001)(82740400003)(40480700001)(82310400005)(26005)(186003)(6666004)(5660300002)(16526019)(426003)(336012)(47076005)(7696005)(36900700001);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Dec 2022 15:29:41.4819 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 1cac1db8-dfbc-4c34-6dc1-08dad93106af 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: BN8NAM11FT036.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB6812 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" In advance of providing support for unaccepted memory, switch from using kmalloc() for allocating the Page State Change (PSC) structure to using a local variable that lives on the stack. This is needed to avoid a possible recursive call into set_pages_state() if the kmalloc() call requires (more) memory to be accepted, which would result in a hang. The current size of the PSC struct is 2,032 bytes. To make the struct more stack friendly, reduce the number of PSC entries from 253 down to 64, resulting in a size of 520 bytes. This is a nice compromise on struct size and total PSC requests while still allowing parallel PSC operations across vCPUs. If the reduction in PSC entries results in any kind of performance issue (that is not seen at the moment), use of a larger static PSC struct, with fallback to the smaller stack version, can be investigated. For more background info on this decision, see the subthread in the Link: tag below. Signed-off-by: Tom Lendacky Link: https://lore.kernel.org/lkml/658c455c40e8950cb046dd885dd19dc1c52d060a= .1659103274.git.thomas.lendacky@amd.com --- arch/x86/include/asm/sev-common.h | 9 +++++++-- arch/x86/kernel/sev.c | 10 ++-------- 2 files changed, 9 insertions(+), 10 deletions(-) diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-c= ommon.h index b8357d6ecd47..8ddfdbe521d4 100644 --- a/arch/x86/include/asm/sev-common.h +++ b/arch/x86/include/asm/sev-common.h @@ -106,8 +106,13 @@ enum psc_op { #define GHCB_HV_FT_SNP BIT_ULL(0) #define GHCB_HV_FT_SNP_AP_CREATION BIT_ULL(1) =20 -/* SNP Page State Change NAE event */ -#define VMGEXIT_PSC_MAX_ENTRY 253 +/* + * SNP Page State Change NAE event + * The VMGEXIT_PSC_MAX_ENTRY determines the size of the PSC structure, w= hich + * is a local stack variable in set_pages_state(). Do not increase this = value + * without evaluating the impact to stack usage. + */ +#define VMGEXIT_PSC_MAX_ENTRY 64 =20 struct psc_hdr { u16 cur_entry; diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index 6b823f913c97..f60733674731 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -880,11 +880,7 @@ static void __set_pages_state(struct snp_psc_desc *dat= a, unsigned long vaddr, static void set_pages_state(unsigned long vaddr, unsigned long npages, int= op) { unsigned long vaddr_end, next_vaddr; - struct snp_psc_desc *desc; - - desc =3D kmalloc(sizeof(*desc), GFP_KERNEL_ACCOUNT); - if (!desc) - panic("SNP: failed to allocate memory for PSC descriptor\n"); + struct snp_psc_desc desc; =20 vaddr =3D vaddr & PAGE_MASK; vaddr_end =3D vaddr + (npages << PAGE_SHIFT); @@ -894,12 +890,10 @@ static void set_pages_state(unsigned long vaddr, unsi= gned long npages, int op) next_vaddr =3D min_t(unsigned long, vaddr_end, (VMGEXIT_PSC_MAX_ENTRY * PAGE_SIZE) + vaddr); =20 - __set_pages_state(desc, vaddr, next_vaddr, op); + __set_pages_state(&desc, vaddr, next_vaddr, op); =20 vaddr =3D next_vaddr; } - - kfree(desc); } =20 void snp_set_memory_shared(unsigned long vaddr, unsigned long npages) --=20 2.38.1