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Re: [Xen-devel] RE: [PATCH 01/13] Nested Virtualization: tools



Dong, Eddie wrote:
Dong, Eddie wrote:
# HG changeset patch
# User cegger
# Date 1283345869 -7200
tools: Add nestedhvm guest config option

diff -r 80ef08613ec2 -r ecec3d163efa tools/libxc/xc_cpuid_x86.c
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -30,7 +30,7 @@
 #define set_bit(idx, dst)   ((dst) |= (1u << ((idx) & 31)))

 #define DEF_MAX_BASE 0x0000000du
-#define DEF_MAX_EXT  0x80000008u
+#define DEF_MAX_EXT  0x8000000au

How can this make Intel CPU happy?
You may refer to my previous comments in V2.
Correct me if I am wrong, but this is only a max boundary:
tools/libxc/xc_cpuid_x86.c:234
    case 0x80000000:
        if ( regs[0] > DEF_MAX_EXT )
            regs[0] = DEF_MAX_EXT;
        break;
So if an Intel CPU returns 0x80000008 here, this will be in the regs[0] field and thus any higher value in DEF_MAX_EXT does not affect the guest's CPUID response. So as long as Intel CPUs don't return higher values which don't match the AMD assignment (which is extremely unlikely), extending DEF_MAX_EXT is fine.

Regards,
Andre.

--
Andre Przywara
AMD-OSRC (Dresden)
Tel: x29712


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