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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, Nadav Amit <nadav.amit@gmail.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>
Subject: [kvm-unit-tests PATCH] cstart64: do not assume CR4 should be zero
Date: Wed, 15 Jul 2020 13:52:35 -0700	[thread overview]
Message-ID: <20200715205235.13113-1-sean.j.christopherson@intel.com> (raw)

Explicitly zero cr4 in prepare_64() instead of "zeroing" it in the
common enter_long_mode().  Clobbering cr4 in enter_long_mode() breaks
switch_to_5level(), which sets cr4.LA57 before calling enter_long_mode()
and obviously expects cr4 to be preserved.

Fixes: d86ef58 ("cstart: do not assume CR4 starts as zero")
Cc: Nadav Amit <namit@vmware.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---

Two lines of code, two bugs.  I'm pretty sure Paolo should win some kind
of award. :-D

 x86/cstart64.S | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/x86/cstart64.S b/x86/cstart64.S
index 3ae98d3..2d16688 100644
--- a/x86/cstart64.S
+++ b/x86/cstart64.S
@@ -175,8 +175,12 @@ prepare_64:
 	lgdt gdt64_desc
 	setup_segments
 
+	xor %eax, %eax
+	mov %eax, %cr4
+
 enter_long_mode:
-	mov $(1 << 5), %eax // pae
+	mov %cr4, %eax
+	bts $5, %eax  // pae
 	mov %eax, %cr4
 
 	mov pt_root, %eax
-- 
2.26.0


             reply	other threads:[~2020-07-15 20:56 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-15 20:52 Sean Christopherson [this message]
2020-07-15 21:46 ` [kvm-unit-tests PATCH] cstart64: do not assume CR4 should be zero Nadav Amit
2020-07-28 21:31   ` Paolo Bonzini
2020-07-28 21:29 ` Paolo Bonzini

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