Re: [edk2-devel] [RFC PATCH 01/28] OvmfPkg/Sec: Enable cache early to speed up booting

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 8/21/19 9:21 AM, Laszlo Ersek wrote:
> On 08/19/19 23:35, Lendacky, Thomas wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> Currently, the OVMF code relies on the hypervisor to enable the cache
>> support on the processor in order to improve the boot speed. However,
>> with SEV-ES, the hypervisor is not allowed to change the CR0 register
>> to enable caching.
>>
>> Update the OVMF Sec support to enable caching in order to improve the
>> boot speed.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>  OvmfPkg/Sec/SecMain.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c
>> index 3914355cd17b..2448be0cd408 100644
>> --- a/OvmfPkg/Sec/SecMain.c
>> +++ b/OvmfPkg/Sec/SecMain.c
>> @@ -739,6 +739,11 @@ SecCoreStartupWithStack (
>>  
>>    ProcessLibraryConstructorList (NULL, NULL);
>>  
>> +  //
>> +  // Enable caching
>> +  //
>> +  AsmEnableCache ();
>> +
>>    DEBUG ((EFI_D_INFO,
>>      "SecCoreStartupWithStack(0x%x, 0x%x)\n",
>>      (UINT32)(UINTN)BootFv,
>>
> 
> This makes me uncomfortable. There used to be problems related to
> caching when VFIO device assignment were used. My concern is admittedly
> vague, but this is a very brittle area of OVMF-on-KVM. If you asked me
> "well what could break here", I'd answer "you never know, and the burden
> of proof is not on me". :) Can we make this change conditional on SEV-ES?
> 

I'll look into that. Anything is possible, just might have to read an MSR
at this stage.

Thanks,
Tom

> Thanks
> Laszlo
>