Hi Andrew,
On 07/03/20 19:22, Andrew Fish via groups.io wrote:
> I noticed for my version of QEMU that MTRR registers are not supported. Is
> that expected? Or is it something if you get wrong it does not break in QEMU?
>
> Due to no MTRR support the CPU Protocol SetMemoeryAttributes() call is
> falling [1] and non of the GCD ranges have EFI_MEMORY_UC Attribute.
>
> I’m not sure but I think the no MTRR case should attempt to set the
> attributes via page tables via:
>
> return AssignMemoryPageAttributes (NULL, BaseAddress, Length,
> MemoryAttributes, NULL);
>
> Vs
>
> return EFI_UNSUPPORTED;
>
> [1]
> https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/CpuDxe/CpuDxe.c#L429
sorry, reaching this email only now.
I wouldn't really expect IsMtrrSupported() to return FALSE.
BOOLEAN
EFIAPI
IsMtrrSupported (
VOID
)
{
CPUID_VERSION_INFO_EDX Edx;
MSR_IA32_MTRRCAP_REGISTER MtrrCap;
//
// Check CPUID(1).EDX[12] for MTRR capability
//
AsmCpuid (CPUID_VERSION_INFO, NULL, NULL, NULL, &Edx.Uint32);
if (Edx.Bits.MTRR == 0) {
return FALSE;
}
//
// Check number of variable MTRRs and fixed MTRRs existence.
// If number of variable MTRRs is zero, or fixed MTRRs do not
// exist, return false.
//
MtrrCap.Uint64 = AsmReadMsr64 (MSR_IA32_MTRRCAP);
if ((MtrrCap.Bits.VCNT == 0) || (MtrrCap.Bits.FIX == 0)) {
return FALSE;
}
return TRUE;
}
In QEMU, the rdmsr is handled in "target/i386/misc_helper.c", function
helper_rdmsr():
case MSR_MTRRcap:
if (env->features[FEAT_1_EDX] & CPUID_MTRR) {
val = MSR_MTRRcap_VCNT | MSR_MTRRcap_FIXRANGE_SUPPORT |
MSR_MTRRcap_WC_SUPPORTED;
} else {
/* XXX: exception? */
val = 0;
}
break;
thus the second "FALSE" branch in IsMtrrSupported() can never be
reached. (Either the first "FALSE" branch is taken, or the "TRUE" branch
is taken.) MSR_MTRRcap_VCNT is 8.
Regarding the first "FALSE" branch, whether that is taken depends on the
QEMU CPU model (or the QEMU command line). Check "target/i386/cpu.c" for
"CPUID_MTRR".
Unfortunately I can't think of an easy way to list the CPU models that
do *not* have CPUID_MTRR. What is your CPU model?
Thanks
Laszlo
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