[Mesa-dev] [Bug 87913] CPU cacheline size of 0 can be returned by CPUID leaf 0x80000006 in some virtual machines

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87913

            Bug ID: 87913
           Summary: CPU cacheline size of 0 can be returned by CPUID leaf
                    0x80000006 in some virtual machines
           Product: Mesa
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: Other
          Assignee: mesa-dev at lists.freedesktop.org
          Reporter: leonid.shatz at ravellosystems.com

In some recent commercial virtual machine environments cache line of 0 was
actually spotted and that resulted in panics and failures of GDM to initialize
leading to the SAD SCREEN.

The code used to provide default nonzero cache line size should be also used in
case when CPU cache line size is extracted from CPUID leaf 0x80000006. 

The following correction is suggested:

src/gallium/auxiliary/util/u_cpu_detect.c:
...
void
util_cpu_detect(void)


    if (regs[0] >= 0x80000006) {
        cpuid(0x80000006, regs2);
+       if (cacheline > 0)
            util_cpu_caps.cacheline = regs2[2] & 0xFF;
    }

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