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[35.79.20.36]) by smtp.gmail.com with ESMTPSA id r17-20020aa79891000000b0052d7cca96acsm3043172pfl.110.2022.08.10.22.21.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Aug 2022 22:21:18 -0700 (PDT) Date: Thu, 11 Aug 2022 05:21:14 +0000 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Aaron Lu Cc: Dave Hansen , Rick Edgecombe , Song Liu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH 1/4] x86/mm/cpa: restore global bit when page is present Message-ID: References: <20220808145649.2261258-1-aaron.lu@intel.com> <20220808145649.2261258-2-aaron.lu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220808145649.2261258-2-aaron.lu@intel.com> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660195280; a=rsa-sha256; cv=none; b=I8LMWr9AqMQ/V2V2+TbPxRJWt2Uk8px5Wg9Od+6/5mnEF38Fj8gmVXAiqueRFb7B19QPk9 UNdp4h8q78p5aRvDcxyqXfuvC3vZaYe4XhjKIMZRxwBKNjY74/3m9XM7kGXFwVnhTt0UIY /714khek7jWj6r/YhuXUPighyHCArFg= ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=hpcD5o2W; spf=pass (imf31.hostedemail.com: domain of 42.hyeyoo@gmail.com designates 209.85.215.182 as permitted sender) smtp.mailfrom=42.hyeyoo@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660195280; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=AQfR77oXK1qGUTAyOmsgC9Pxbg9bnSvs4vH+7LPgnRU=; b=8Ww6JwjdZDvvpwmo29XEZcLSmglBcZ09dmeI4TiL2ImhGphVIFdcMwrjZzAq2X/l0KhBIR angDDYJSc4RCm9qW1tdGN8SoRJPEewfIXgrshjdi03FbuOSp5WJBMdUa85aRDq9X/aL7k3 Q3VJzH8KNti55T3+Ap2N3honiAPtrYQ= X-Stat-Signature: w6dbcqcmctgnwj3c1jwjy564cacsj4iq X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 9119F2017F Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=hpcD5o2W; spf=pass (imf31.hostedemail.com: domain of 42.hyeyoo@gmail.com designates 209.85.215.182 as permitted sender) smtp.mailfrom=42.hyeyoo@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspam-User: X-HE-Tag: 1660195280-682251 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Aug 08, 2022 at 10:56:46PM +0800, Aaron Lu wrote: > For configs that don't have PTI enabled or cpus that don't need > meltdown mitigation, current kernel can lose GLOBAL bit after a page > goes through a cycle of present -> not present -> present. > > It happened like this(__vunmap() does this in vm_remove_mappings()): > original page protection: 0x8000000000000163 (NX/G/D/A/RW/P) > set_memory_np(page, 1): 0x8000000000000062 (NX/D/A/RW) lose G and P > set_memory_p(pagem 1): 0x8000000000000063 (NX/D/A/RW/P) restored P > > In the end, this page's protection no longer has Global bit set and this > would create problem for this merge small mapping feature. > > For this reason, restore Global bit for systems that do not have PTI > enabled if page is present. > > (pgprot_clear_protnone_bits() deserves a better name if this patch is > acceptible but first, I would like to get some feedback if this is the > right way to solve this so I didn't bother with the name yet) > > Signed-off-by: Aaron Lu > --- > arch/x86/mm/pat/set_memory.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c > index 1abd5438f126..33657a54670a 100644 > --- a/arch/x86/mm/pat/set_memory.c > +++ b/arch/x86/mm/pat/set_memory.c > @@ -758,6 +758,8 @@ static pgprot_t pgprot_clear_protnone_bits(pgprot_t prot) > */ > if (!(pgprot_val(prot) & _PAGE_PRESENT)) > pgprot_val(prot) &= ~_PAGE_GLOBAL; > + else > + pgprot_val(prot) |= _PAGE_GLOBAL & __default_kernel_pte_mask; > > return prot; > } IIUC It makes it unable to set _PAGE_GLOBL when PTI is on. Maybe it would be less intrusive to make set_direct_map_default_noflush() replace protection bits with PAGE_KENREL as it's only called for direct map, and the function is to reset permission to default: diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 1abd5438f126..0dd4433c1382 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -2250,7 +2250,16 @@ int set_direct_map_invalid_noflush(struct page *page) int set_direct_map_default_noflush(struct page *page) { - return __set_pages_p(page, 1); + unsigned long tempaddr = (unsigned long) page_address(page); + struct cpa_data cpa = { + .vaddr = &tempaddr, + .pgd = NULL, + .numpages = 1, + .mask_set = PAGE_KERNEL, + .mask_clr = __pgprot(~0), + .flags = 0}; + + return __change_page_attr_set_clr(&cpa, 0); } set_direct_map_{invalid,default}_noflush() is the exact reason why direct map become split after vmalloc/vfree with special permissions. > -- > 2.37.1 > >