linux-kernel - [PATCHv4 4/5] kvm: eoi msi documentation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <83448488f2e7220e96e9bedce870c139c712a9ad.1337168687.git.mst@redhat.com>
Date:	Wed, 16 May 2012 14:46:23 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	x86@...nel.org, kvm@...r.kernel.org
Cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, gleb@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCHv4 4/5] kvm: eoi msi documentation

Document the new EOI MSR. Couldn't decide whether this change belongs
conceptually on guest or host side, so a separate patch.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 Documentation/virtual/kvm/msr.txt |   32 ++++++++++++++++++++++++++++++++
 1 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/Documentation/virtual/kvm/msr.txt b/Documentation/virtual/kvm/msr.txt
index 5031780..3481f1b 100644
--- a/Documentation/virtual/kvm/msr.txt
+++ b/Documentation/virtual/kvm/msr.txt
@@ -219,3 +219,35 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
 		steal: the amount of time in which this vCPU did not run, in
 		nanoseconds. Time during which the vcpu is idle, will not be
 		reported as steal time.
+
+MSR_KVM_EOI_EN: 0x4b564d04
+	data: Bit 0 is 1 when PV end of interrupt is enabled on the vcpu; 0
+	when disabled.  When enabled, bits 63-1 hold 2-byte aligned physical address
+	of a 2 byte memory area which must be in guest RAM and must be zeroed.
+
+	The first, least significant bit of 2 byte memory location will be
+	written to by the hypervisor, typically at the time of interrupt
+	injection.  Value of 1 means that guest can skip writing EOI to the apic
+	(using MSR or MMIO write); instead, it is sufficient to signal
+	EOI by clearing the bit in guest memory - this location will
+	later be polled by the hypervisor.
+	Value of 0 means that the EOI write is required.
+
+	It is always safe for the guest to ignore the optimization and perform
+	the APIC EOI write anyway.
+
+	Hypervisor is guaranteed to only modify this least
+	significant bit while in the current VCPU context, this means that
+	guest does not need to use either lock prefix or memory ordering
+	primitives to synchronise with the hypervisor.
+
+	However, hypervisor can set and clear this memory bit at any time:
+	therefore to make sure hypervisor does not interrupt the
+	guest and clear the least significant bit in the memory area
+	in the window between guest testing it to detect
+	whether it can skip EOI apic write and between guest
+	clearing it to signal EOI to the hypervisor,
+	guest must both read the least sgnificant bit in the memory area and
+	clear it using a single CPU instruction, such as test and clear, or
+	compare and exchange.
+
-- 
MST

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/