From: Michael Kelley <mhklinux@outlook.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"ardb@kernel.org" <ardb@kernel.org>,
"hch@infradead.org" <hch@infradead.org>,
"Lutomirski, Andy" <luto@kernel.org>,
"linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
"haiyangz@microsoft.com" <haiyangz@microsoft.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"kirill.shutemov@linux.intel.com"
<kirill.shutemov@linux.intel.com>,
"mingo@redhat.com" <mingo@redhat.com>,
"seanjc@google.com" <seanjc@google.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kys@microsoft.com" <kys@microsoft.com>,
"Cui, Dexuan" <decui@microsoft.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"urezki@gmail.com" <urezki@gmail.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
"bp@alien8.de" <bp@alien8.de>, "Rodel, Jorg" <jroedel@suse.de>,
"sathyanarayanan.kuppuswamy@linux.intel.com"
<sathyanarayanan.kuppuswamy@linux.intel.com>,
"lstoakes@gmail.com" <lstoakes@gmail.com>,
"x86@kernel.org" <x86@kernel.org>
Subject: RE: [PATCH v2 2/8] x86/mm: Don't do a TLB flush if changing a PTE that isn't marked present
Date: Tue, 28 Nov 2023 17:34:38 +0000 [thread overview]
Message-ID: <SN6PR02MB41573431683896536879EF40D4BCA@SN6PR02MB4157.namprd02.prod.outlook.com> (raw)
In-Reply-To: <4a64d05c80c9c490d291af881a86c3d853160060.camel@intel.com>
From: Edgecombe, Rick P <rick.p.edgecombe@intel.com> Sent: Monday, November 27, 2023 2:21 PM
>
> On Tue, 2023-11-21 at 13:20 -0800, mhkelley58@gmail.com wrote:
> > --- a/arch/x86/mm/pat/set_memory.c
> > +++ b/arch/x86/mm/pat/set_memory.c
> > @@ -1636,7 +1636,10 @@ static int __change_page_attr(struct cpa_data
> > *cpa, int primary)
> > */
> > if (pte_val(old_pte) != pte_val(new_pte)) {
> > set_pte_atomic(kpte, new_pte);
> > - cpa->flags |= CPA_FLUSHTLB;
> > +
> > + /* If old_pte isn't present, it's not in the TLB */
> > + if (pte_present(old_pte))
> > + cpa->flags |= CPA_FLUSHTLB;
> > }
> > cpa->numpages = 1;
> > return 0;
> >
>
> Makes sense to me. The PMD case can be handled similarly in
> __should_split_large_page().
OK, I'll look at that case.
>
> I also think it should be more robust in regards to the cache flushing
> changes.
>
> If callers did:
> set_memory_np()
> set_memory_uc()
> set_memory_p()
>
> Then the cache flush would be missed. I don't think anyone is, but we
> shouldn't introduce hidden things like that. Maybe fix it like this:
>
> diff --git a/arch/x86/mm/pat/set_memory.c
> b/arch/x86/mm/pat/set_memory.c
> index f519e5ca543b..28ff53a4447a 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -1856,11 +1856,6 @@ static int change_page_attr_set_clr(unsigned
> long *addr, int numpages,
>
> ret = __change_page_attr_set_clr(&cpa, 1);
>
> - /*
> - * Check whether we really changed something:
> - */
> - if (!(cpa.flags & CPA_FLUSHTLB))
> - goto out;
>
> /*
> * No need to flush, when we did not set any of the caching
> @@ -1868,6 +1863,12 @@ static int change_page_attr_set_clr(unsigned
> long *addr, int numpages,
> */
> cache = !!pgprot2cachemode(mask_set);
>
> + /*
> + * Check whether we really changed something:
> + */
> + if (!(cpa.flags & CPA_FLUSHTLB) && !cache)
> + goto out;
> +
> /*
> * On error; flush everything to be sure.
> */
>
> Hmm, might want to maintain the "On error; flush everything to be sure"
> logic in the NP->P case as well.
OK, I see your point. I had not realized that CPA_FLUSHTLB really
has a meaning beyond just indicating that the TLB needs to be
flushed. It really means "something has changed" in a PTE. I'll
incorporate your suggestion.
Michael
next prev parent reply other threads:[~2023-11-28 17:34 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-21 21:20 [PATCH v2 0/8] x86/coco: Mark CoCo VM pages not present when changing encrypted state mhkelley58
2023-11-21 21:20 ` [PATCH v2 1/8] x86/coco: Use slow_virt_to_phys() in page transition hypervisor callbacks mhkelley58
2023-11-21 21:20 ` [PATCH v2 2/8] x86/mm: Don't do a TLB flush if changing a PTE that isn't marked present mhkelley58
2023-11-27 22:21 ` Edgecombe, Rick P
2023-11-28 17:34 ` Michael Kelley [this message]
2023-11-21 21:20 ` [PATCH v2 3/8] x86/mm: Remove "static" from vmap_pages_range() mhkelley58
2023-11-22 6:26 ` Christoph Hellwig
2023-11-23 0:24 ` Michael Kelley
2023-11-23 7:32 ` Christoph Hellwig
2023-11-27 1:06 ` Michael Kelley
2023-11-21 21:20 ` [PATCH v2 4/8] x86/sev: Enable PVALIDATE for PFNs without a valid virtual address mhkelley58
2023-11-27 21:38 ` Edgecombe, Rick P
2023-11-28 18:08 ` Michael Kelley
2023-11-28 18:59 ` Edgecombe, Rick P
2023-12-12 18:35 ` Michael Kelley
2023-11-21 21:20 ` [PATCH v2 5/8] x86/mm: Mark CoCo VM pages not present while changing encrypted state mhkelley58
2023-11-21 21:20 ` [PATCH v2 6/8] x86/mm: Merge CoCo prepare and finish hypervisor callbacks mhkelley58
2023-11-21 21:20 ` [PATCH v2 7/8] x86/mm: Remove unnecessary call layer for __set_memory_enc_pgtable() mhkelley58
2023-11-21 21:20 ` [PATCH v2 8/8] x86/mm: Add comments about errors in set_memory_decrypted()/encrypted() mhkelley58
2023-11-24 10:06 ` [PATCH v2 0/8] x86/coco: Mark CoCo VM pages not present when changing encrypted state kirill.shutemov
2023-11-28 19:12 ` Michael Kelley
2023-11-29 15:10 ` kirill.shutemov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=SN6PR02MB41573431683896536879EF40D4BCA@SN6PR02MB4157.namprd02.prod.outlook.com \
--to=mhklinux@outlook.com \
--cc=akpm@linux-foundation.org \
--cc=ardb@kernel.org \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=decui@microsoft.com \
--cc=haiyangz@microsoft.com \
--cc=hch@infradead.org \
--cc=hpa@zytor.com \
--cc=jroedel@suse.de \
--cc=kirill.shutemov@linux.intel.com \
--cc=kys@microsoft.com \
--cc=linux-coco@lists.linux.dev \
--cc=linux-hyperv@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=lstoakes@gmail.com \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rick.p.edgecombe@intel.com \
--cc=sathyanarayanan.kuppuswamy@linux.intel.com \
--cc=seanjc@google.com \
--cc=tglx@linutronix.de \
--cc=thomas.lendacky@amd.com \
--cc=urezki@gmail.com \
--cc=wei.liu@kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).