From: Jan Beulich <jbeulich@suse.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org,
Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
George Dunlap <george.dunlap@citrix.com>,
Ian Jackson <iwj@xenproject.org>, Julien Grall <julien@xen.org>,
Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [PATCH] x86/msr: fix handling of MSR_IA32_PERF_{STATUS/CTL}
Date: Tue, 13 Oct 2020 15:49:37 +0200 [thread overview]
Message-ID: <edc93f6b-4770-baed-9d00-428bce47e30b@suse.com> (raw)
In-Reply-To: <20201006162327.93055-1-roger.pau@citrix.com>
On 06.10.2020 18:23, Roger Pau Monne wrote:
> Currently a PV hardware domain can also be given control over the CPU
> frequency, and such guest is allowed to write to MSR_IA32_PERF_CTL.
> However since commit 322ec7c89f6 the default behavior has been changed
> to reject accesses to not explicitly handled MSRs, preventing PV
> guests that manage CPU frequency from reading
> MSR_IA32_PERF_{STATUS/CTL}.
>
> Additionally some HVM guests (Windows at least) will attempt to read
> MSR_IA32_PERF_CTL and will panic if given back a #GP fault:
>
> vmx.c:3035:d8v0 RDMSR 0x00000199 unimplemented
> d8v0 VIRIDIAN CRASH: 3b c0000096 fffff806871c1651 ffffda0253683720 0
>
> Move the handling of MSR_IA32_PERF_{STATUS/CTL} to the common MSR
> handling shared between HVM and PV guests, and add an explicit case
> for reads to MSR_IA32_PERF_{STATUS/CTL}.
>
> Restore previous behavior and allow PV guests with the required
> permissions to read the contents of the mentioned MSRs. Non privileged
> guests will get 0 when trying to read those registers, as writes to
> MSR_IA32_PERF_CTL by such guest will already be silently dropped.
>
> Fixes: 322ec7c89f6 ('x86/pv: disallow access to unknown MSRs')
> Fixes: 84e848fd7a1 ('x86/hvm: disallow access to unknown MSRs')
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
I would have given this my R-b, but Andrew's "straight up broken"
comment needs resolving first, one way or another.
Jan
prev parent reply other threads:[~2020-10-13 13:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-06 16:23 [PATCH] x86/msr: fix handling of MSR_IA32_PERF_{STATUS/CTL} Roger Pau Monne
2020-10-07 12:06 ` Andrew Cooper
2020-10-07 16:41 ` Roger Pau Monné
2020-10-13 13:44 ` Jan Beulich
2020-10-15 13:34 ` Roger Pau Monné
2020-11-09 13:21 ` Roger Pau Monné
2020-10-13 13:49 ` Jan Beulich [this message]
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