From: Michael Kelley <mikelley@microsoft.com>
To: linux-kernel@vger.kernel.org, tglx@linutronix.de,
peterz@infradead.org, kys@microsoft.com, sthemmin@microsoft.com,
wei.liu@kernel.org, mingo@redhat.com, bp@alien8.de,
x86@kernel.org, hpa@zytor.com, linux-hyperv@vger.kernel.org
Cc: mikelley@microsoft.com
Subject: [PATCH 1/1] x86/hyperv: Clarify comment on x2apic mode
Date: Mon, 26 Oct 2020 07:52:52 -0700 [thread overview]
Message-ID: <1603723972-81303-1-git-send-email-mikelley@microsoft.com> (raw)
The comment about Hyper-V accessors is unclear regarding their
potential use in x2apic mode, as is the associated commit message
in e211288b72f1. Clarify that while the architectural and
synthetic MSRs are equivalent in x2apic mode, the full set of xapic
accessors cannot be used because of register layout differences.
Fixes: e211288b72f1 ("x86/hyperv: Make vapic support x2apic mode")
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
---
arch/x86/hyperv/hv_apic.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index 40e0e32..284e736 100644
--- a/arch/x86/hyperv/hv_apic.c
+++ b/arch/x86/hyperv/hv_apic.c
@@ -273,11 +273,15 @@ void __init hv_apic_init(void)
pr_info("Hyper-V: Using enlightened APIC (%s mode)",
x2apic_enabled() ? "x2apic" : "xapic");
/*
- * With x2apic, architectural x2apic MSRs are equivalent to the
- * respective synthetic MSRs, so there's no need to override
- * the apic accessors. The only exception is
- * hv_apic_eoi_write, because it benefits from lazy EOI when
- * available, but it works for both xapic and x2apic modes.
+ * When in x2apic mode, don't use the Hyper-V specific APIC
+ * accessors since the field layout in the ICR register is
+ * different in x2apic mode. Furthermore, the architectural
+ * x2apic MSRs function just as well as the Hyper-V
+ * synthetic APIC MSRs, so there's no benefit in having
+ * separate Hyper-V accessors for x2apic mode. The only
+ * exception is hv_apic_eoi_write, because it benefits from
+ * lazy EOI when available, but the same accessor works for
+ * both xapic and x2apic because the field layout is the same.
*/
apic_set_eoi_write(hv_apic_eoi_write);
if (!x2apic_enabled()) {
--
1.8.3.1
next reply other threads:[~2020-10-26 14:53 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-26 14:52 Michael Kelley [this message]
2020-10-26 16:29 ` [PATCH 1/1] x86/hyperv: Clarify comment on x2apic mode Wei Liu
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=1603723972-81303-1-git-send-email-mikelley@microsoft.com \
--to=mikelley@microsoft.com \
--cc=bp@alien8.de \
--cc=hpa@zytor.com \
--cc=kys@microsoft.com \
--cc=linux-hyperv@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=sthemmin@microsoft.com \
--cc=tglx@linutronix.de \
--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).