On 2/14/22 15:03, Igor Mammedov wrote:
> On Mon, 7 Feb 2022 20:24:21 +0000
> Joao Martins <joao.m.mart...@oracle.com> wrote:
>
>> Default phys-bits on Qemu is TCG_PHYS_BITS (40) which is enough
>> to address 1Tb (0xff ffff ffff). On AMD platforms, if a
>> ram-above-4g relocation happens and the CPU wasn't configured
>> with a big enough phys-bits, warn the user. There isn't a
>> catastrophic failure exactly, the guest will still boot, but
>> most likely won't be able to use more than ~4G of RAM.
>
> how 'unable to use" would manifest?
> It might be better to prevent QEMU startup with broken setup (CLI)
> rather then letting guest run and trying to figure out what's
> going wrong when users start to complain.
>
Sounds better to be conservative here.
I will change from warn_report() to error_report()
and exit.
>>
>> Signed-off-by: Joao Martins <joao.m.mart...@oracle.com>
>> ---
>> hw/i386/pc.c | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
>> index b060aedd38f3..f8712eb8427e 100644
>> --- a/hw/i386/pc.c
>> +++ b/hw/i386/pc.c
>> @@ -842,6 +842,7 @@ static void relocate_4g(MachineState *machine,
>> PCMachineState *pcms)
>> X86MachineState *x86ms = X86_MACHINE(pcms);
>> ram_addr_t device_mem_size = 0;
>> uint32_t eax, vendor[3];
>> + hwaddr maxphysaddr;
>>
>> host_cpuid(0x0, 0, &eax, &vendor[0], &vendor[2], &vendor[1]);
>> if (!IS_AMD_VENDOR(vendor)) {
>> @@ -858,6 +859,12 @@ static void relocate_4g(MachineState *machine,
>> PCMachineState *pcms)
>> return;
>> }
>>
>> + maxphysaddr = ((hwaddr)1 << X86_CPU(first_cpu)->phys_bits) - 1;
>> + if (maxphysaddr < AMD_ABOVE_1TB_START)
>> + warn_report("Relocated RAM above 4G to start at %lu "
>> + "phys-bits too low (%u)",
>> + AMD_ABOVE_1TB_START, X86_CPU(first_cpu)->phys_bits);
>
> perhaps this hunk belongs to the end of pc_memory_init(),
> it's not HT fixup specific at all?
>
It is HT fixup related. Because we are relocating the whole above-4g-ram,
on what used to be enough with just 40 phys bits (default).
> Also I'm not sure but there are host_phys_bits/host_phys_bits_limit
> properties,
> perhaps they need to be checked/verified as well
When booted with +host-phys-bits and/or with a host-phys-bits-limit=X, the
@phys_bits
value will be either set to host, and ultimately bound to a maximum of
host_phys_bits_limit (if at all set).
So essentially the selected phys_bits that we're checking above is the only
thing
we need to care about IIUC.
