35 lines
1.3 KiB
Diff
35 lines
1.3 KiB
Diff
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Legacy hypervisors (RHEL 5.0 and RHEL 5.1) do not handle guest writes to
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cr4 gracefully. If a guest attempts to write a bit of cr4 that is
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unsupported, then the HV is so offended it crashes the domain. While
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later guest kernels (such as RHEL6) don't assume the HV supports all
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features, they do expect nicer responses. That assumption introduced
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code that probes whether or not xsave is supported early in the boot. So
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now when attempting to boot a RHEL6 guest on RHEL5.0 or RHEL5.1 an early
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crash will occur.
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This patch is quite obviously an undesirable hack. The real fix for this
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problem should be in the HV, and is, in later HVs. However, to support
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running on old HVs, RHEL6 can take this small change. No impact will
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occur for running on any RHEL HV (not even RHEL 5.5 supports xsave).
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There is only potential for guest performance loss on upstream Xen.
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---
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arch/x86/xen/enlighten.c | 1 +
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1 files changed, 1 insertions(+), 0 deletions(-)
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diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
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index 52f8e19..6db3d67 100644
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--- a/arch/x86/xen/enlighten.c
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+++ b/arch/x86/xen/enlighten.c
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@@ -802,6 +802,7 @@ static void xen_write_cr4(unsigned long cr4)
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{
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cr4 &= ~X86_CR4_PGE;
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cr4 &= ~X86_CR4_PSE;
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+ cr4 &= ~X86_CR4_OSXSAVE;
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native_write_cr4(cr4);
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}
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--
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1.6.6.1
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