linux-kernel - [PATCH v2 0/8] x86/mtrr: fix handling with PAT but without MTRR

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Date:   Thu,  9 Feb 2023 08:22:12 +0100
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-hyperv@...r.kernel.org
Cc:     lists@...dbynature.de, mikelley@...rosoft.com,
        torvalds@...ux-foundation.org, Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v2 0/8] x86/mtrr: fix handling with PAT but without MTRR

This series tries to fix the rather special case of PAT being available
without having MTRRs (either due to CONFIG_MTRR being not set, or
because the feature has been disabled e.g. by a hypervisor).

The main use cases are Xen PV guests and SEV-SNP guests running under
Hyper-V.

Instead of trying to work around all the issues by adding if statements
here and there, just try to use the complete available infrastructure
by setting up a read-only MTRR state when needed.

In the Xen PV case the current MTRR MSR values can be read from the
hypervisor, while for the SEV-SNP case all needed is to set the
default caching mode to "WB".

I have added more cleanup which has been discussed when looking into
the most recent failures.

Note that I couldn't test the Hyper-V related change (patch 3).

Running on bare metal and with Xen didn't show any problems with the
series applied.

Changes in V2:
- replaced former patches 1+2 with new patches 1-4, avoiding especially
  the rather hacky approach of V1, while making all the MTRR type
  conflict tests available for the Xen PV case
- updated patch 6 (was patch 4 in V1)

Juergen Gross (8):
  x86/mtrr: split off physical address size calculation
  x86/mtrr: support setting MTRR state for software defined MTRRs
  x86/hyperv: set MTRR state when running as SEV-SNP Hyper-V guest
  x86/xen: set MTRR state when running as Xen PV initial domain
  x86/mtrr: revert commit 90b926e68f50
  x86/mtrr: don't let mtrr_type_lookup() return MTRR_TYPE_INVALID
  x86/mm: only check uniform after calling mtrr_type_lookup()
  x86/mtrr: drop sanity check in mtrr_type_lookup_fixed()

 arch/x86/include/asm/mtrr.h        |  9 +++-
 arch/x86/include/uapi/asm/mtrr.h   |  6 +--
 arch/x86/kernel/cpu/mshyperv.c     |  8 +++
 arch/x86/kernel/cpu/mtrr/generic.c | 56 +++++++++++++++++----
 arch/x86/kernel/cpu/mtrr/mtrr.c    | 79 ++++++++++++++++--------------
 arch/x86/mm/pat/memtype.c          |  3 +-
 arch/x86/mm/pgtable.c              |  6 +--
 arch/x86/xen/enlighten_pv.c        | 49 ++++++++++++++++++
 8 files changed, 159 insertions(+), 57 deletions(-)

-- 
2.35.3