From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C39042C80 for ; Mon, 3 Jan 2022 18:11:00 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id E884A210E8; Mon, 3 Jan 2022 18:10:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1641233458; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Op3ImOqOwCCgnIZralyZf3tGTao+t3Y622jP3bRdc3M=; b=C2zVimxxGBkbjHiUPECVcDKFMB2sv4FqZcW8GgohA812H99T/sYphGZEA629myHI1xwfUB EAkGvy3QcUL7w4mnTnl7szW5Fx/6/jwA9fnzECUU2Sma7xvOTmQrTquQlS23TiIHyoVOdi hXjehu5D/56NRpJ+CiRwuwIH541HAPU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1641233458; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Op3ImOqOwCCgnIZralyZf3tGTao+t3Y622jP3bRdc3M=; b=oSr9zFj9HMCbLGX5MoS/SaS6qozzC73ylXqxLdax9DGQnykLDDk2KqDo7iHeTOHc038jY8 783kriuIq+Bu45Bg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 7535E13B09; Mon, 3 Jan 2022 18:10:58 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id UEjgGzI802FfKwAAMHmgww (envelope-from ); Mon, 03 Jan 2022 18:10:58 +0000 Message-ID: <91eb34b0-ff19-40a3-9744-ad80432d8317@suse.cz> Date: Mon, 3 Jan 2022 19:10:58 +0100 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Content-Language: en-US To: Borislav Petkov , Brijesh Singh Cc: x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, Thomas Gleixner , Ingo Molnar , Joerg Roedel , Tom Lendacky , "H. Peter Anvin" , Ard Biesheuvel , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Jim Mattson , Andy Lutomirski , Dave Hansen , Sergio Lopez , Peter Gonda , Peter Zijlstra , Srinivas Pandruvada , David Rientjes , Dov Murik , Tobin Feldman-Fitzthum , Michael Roth , "Kirill A . Shutemov" , Andi Kleen , "Dr . David Alan Gilbert" , tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com References: <20211210154332.11526-1-brijesh.singh@amd.com> <20211210154332.11526-21-brijesh.singh@amd.com> From: Vlastimil Babka Subject: Re: [PATCH v8 20/40] x86/sev: Use SEV-SNP AP creation to start secondary CPUs In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/31/21 16:36, Borislav Petkov wrote: > On Fri, Dec 10, 2021 at 09:43:12AM -0600, Brijesh Singh wrote: >> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h >> index 123a96f7dff2..38c14601ae4a 100644 > >> +{ >> + unsigned long pfn; >> + struct page *p; >> + >> + /* >> + * Allocate an SNP safe page to workaround the SNP erratum where >> + * the CPU will incorrectly signal an RMP violation #PF if a >> + * hugepage (2mb or 1gb) collides with the RMP entry of VMSA page. > > 2MB or 1GB > > Collides how? The 4K frame is inside the hugepage? > >> + * The recommeded workaround is to not use the large page. > > Unknown word [recommeded] in comment, suggestions: > ['recommended', 'recommend', 'recommitted', 'commended', 'commandeered'] > >> + * >> + * Allocate one extra page, use a page which is not 2mb aligned > > 2MB-aligned > >> + * and free the other. >> + */ >> + p = alloc_pages(GFP_KERNEL_ACCOUNT | __GFP_ZERO, 1); >> + if (!p) >> + return NULL; >> + >> + split_page(p, 1); >> + >> + pfn = page_to_pfn(p); >> + if (IS_ALIGNED(__pfn_to_phys(pfn), PMD_SIZE)) { >> + pfn++; >> + __free_page(p); >> + } else { >> + __free_page(pfn_to_page(pfn + 1)); >> + } > > AFAICT, this is doing all this stuff so that you can make sure you get a > non-2M-aligned page. I wonder if there's a way to simply ask mm to give > you such page directly. > > vbabka? AFAIK, not, as this is a very unusual constraint. Unless there are more places that need it, should be fine to solve it like above. Maybe just also be optimistic and try a plain order-0 first and only if it has the undesired alignment (which should happen only once per 512 allocations), fallback to the above?