From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Barret Rhoden <brho@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
David Hildenbrand <david@redhat.com>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
linux-nvdimm@lists.01.org, x86@kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, jason.zeng@intel.com
Subject: Re: [PATCH v5 1/2] mm: make dev_pagemap_mapping_shift() externally visible
Date: Tue, 17 Dec 2019 16:18:57 -0800 [thread overview]
Message-ID: <20191218001857.GM11771@linux.intel.com> (raw)
In-Reply-To: <e004e742-f755-c22c-57bb-acfe30971c7d@google.com>
On Mon, Dec 16, 2019 at 12:59:53PM -0500, Barret Rhoden wrote:
> On 12/13/19 12:47 PM, Sean Christopherson wrote:
> >>+EXPORT_SYMBOL_GPL(dev_pagemap_mapping_shift);
> >
> >This is basically a rehash of lookup_address_in_pgd(), and doesn't provide
> >exactly what KVM needs. E.g. KVM works with levels instead of shifts, and
> >it would be nice to provide the pte so that KVM can sanity check that the
> >pfn from this walk matches the pfn it plans on mapping.
>
> One minor issue is that the levels for lookup_address_in_pgd() and for KVM
> differ in name, although not in value. lookup uses PG_LEVEL_4K = 1. KVM
> uses PT_PAGE_TABLE_LEVEL = 1. The enums differ a little too: x86 has a name
> for a 512G page, etc. It's all in arch/x86.
>
> Does KVM-x86 need its own names for the levels? If not, I could convert the
> PT_PAGE_TABLE_* stuff to PG_LEVEL_* stuff.
Not really. I suspect the whole reason KVM has different enums is to
handle PSE/Mode-B paging, where PG_LEVEL_2M would be inaccurate, e.g.:
if (PTTYPE == 32 && walker->level == PT_DIRECTORY_LEVEL && is_cpuid_PSE36())
gfn += pse36_gfn_delta(pte);
That being said, I absolute loathe PT_PAGE_TABLE_LEVEL, I can never
remember that it means 4k pages. I would be in favor of using the kernel's
enums with some KVM-specific abstraction of PG_LEVEL_2M, e.g.
/* KVM Hugepage definitions for x86 */
enum {
PG_LEVEL_2M_OR_4M = PG_LEVEL_2M,
/* set max level to the biggest one */
KVM_MAX_HUGEPAGE_LEVEL = PG_LEVEL_1G,
};
And ideally restrict usage of the ugly PG_LEVEL_2M_OR_4M to flows that can
actually encounter 4M pages, i.e. when walking guest page tables. On the
host side, KVM always uses PAE or 64-bit paging.
Personally, I'd pursue that in a separate patch/series, it'll touch a
massive amount of code and will probably get bikeshedded a fair amount.
_______________________________________________
Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
To unsubscribe send an email to linux-nvdimm-leave@lists.01.org
next prev parent reply other threads:[~2019-12-18 0:19 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-12 18:22 [PATCH v5 0/2] kvm: Use huge pages for DAX-backed files Barret Rhoden
2019-12-12 18:22 ` [PATCH v5 1/2] mm: make dev_pagemap_mapping_shift() externally visible Barret Rhoden
2019-12-13 17:47 ` Sean Christopherson
2019-12-13 18:13 ` Dan Williams
2019-12-16 17:59 ` Barret Rhoden
2019-12-18 0:18 ` Sean Christopherson [this message]
2020-01-15 18:33 ` Paolo Bonzini
2019-12-12 18:22 ` [PATCH v5 2/2] kvm: Use huge pages for DAX-backed files Barret Rhoden
2019-12-12 18:47 ` Liran Alon
2019-12-12 18:49 ` Liran Alon
2019-12-12 19:55 ` Barret Rhoden
2019-12-13 1:07 ` Liran Alon
2019-12-13 14:13 ` Barret Rhoden
2019-12-13 17:19 ` Sean Christopherson
2019-12-13 17:31 ` Liran Alon
2019-12-13 17:50 ` Sean Christopherson
2019-12-13 18:08 ` Liran Alon
2019-12-16 16:05 ` Barret Rhoden
2020-01-07 19:05 ` Sean Christopherson
2020-01-07 19:19 ` Barret Rhoden
2020-01-08 1:20 ` Sean Christopherson
2020-01-08 1:39 ` Dan Williams
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=20191218001857.GM11771@linux.intel.com \
--to=sean.j.christopherson@intel.com \
--cc=alexander.h.duyck@linux.intel.com \
--cc=brho@google.com \
--cc=david@redhat.com \
--cc=jason.zeng@intel.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-nvdimm@lists.01.org \
--cc=pbonzini@redhat.com \
--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).