linux-kernel - [PATCH 0/6] xen/x86: PV boot speedup

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Date:   Thu, 30 Sep 2021 14:33:20 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: [PATCH 0/6] xen/x86: PV boot speedup

The observed (by the human eye) performance difference of early boot
between native and PV-on-Xen was just too large to not look into. As
it turns out, gaining performance back wasn't all that difficult.

While the series (re)introduces a small number of PTWR emulations on
the boot path (from phys_pte_init()), there has been a much larger
number of them post-boot. Hence I think if this was of concern, the
post-boot instances would want eliminating first.

Some of the later changes aren'r directly related to the main goal of
the series; these address aspects noticed while doing the investigation.

1: streamline set_pte_mfn()
2: restore (fix) xen_set_pte_init() behavior
3: adjust xen_set_fixmap()
4: adjust handling of the L3 user vsyscall special page table
5: there's no highmem anymore in PV mode
6: restrict PV Dom0 identity mapping

Jan