linux-kernel - Re: [PATCH] x86/sev-es: Expose __sev_es_ghcb_hv_call() to call ghcb hv call out of sev code

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Date:   Wed, 20 Oct 2021 22:23:06 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...en8.de>
Cc:     Tianyu Lan <Tianyu.Lan@...rosoft.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
        x86@...nel.org, hpa@...or.com, dave.hansen@...ux.intel.com,
        luto@...nel.org, peterz@...radead.org, davem@...emloft.net,
        kuba@...nel.org, gregkh@...uxfoundation.org, arnd@...db.de,
        jroedel@...e.de, brijesh.singh@....com, pgonda@...gle.com,
        akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        rppt@...nel.org, tj@...nel.org, aneesh.kumar@...ux.ibm.com,
        saravanand@...com, hannes@...xchg.org, rientjes@...gle.com,
        michael.h.kelley@...rosoft.com, linux-arch@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, vkuznets@...hat.com,
        konrad.wilk@...cle.com, hch@....de, robin.murphy@....com,
        joro@...tes.org, parri.andrea@...il.com, dave.hansen@...el.com
Subject: Re: [PATCH] x86/sev-es: Expose __sev_es_ghcb_hv_call() to call ghcb
 hv call out of sev code




On 10/20/2021 9:56 PM, Tom Lendacky wrote:
> On 10/20/21 8:39 AM, Borislav Petkov wrote:
>> On Wed, Oct 20, 2021 at 08:39:59PM +0800, Tianyu Lan wrote:
>>> Hyper-V runs paravisor in guest VMPL0 which emulates some functions
>>> (e.g, timer, tsc, serial console and so on) via handling VC exception.
>>> GHCB pages are allocated and set up by the paravisor and report to Linux
>>> guest via MSR register.Hyper-V SEV implementation is unenlightened guest
>>> case which doesn't Linux doesn't handle VC and paravisor in the VMPL0
>>> handle it.
>>
>> Aha, unenlightened.
>>
>> So why don't you export the original function by doing this (only
>> partial diff to show intent only):

This follows Joreg's previous comment and I implemented similar version 
in the V! patchset([PATCH 05/13] HV: Add Write/Read MSR registers via 
ghcb page https://lkml.org/lkml/2021/7/28/668).
"Instead, factor out a helper function which contains what Hyper-V needs 
and use that in sev_es_ghcb_hv_call() and Hyper-V code."

https://lkml.org/lkml/2021/8/2/375

>>
>> ---
>> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
>> index f1d513897baf..bfe82f58508f 100644
>> --- a/arch/x86/kernel/sev-shared.c
>> +++ b/arch/x86/kernel/sev-shared.c
>> @@ -125,7 +125,7 @@ static enum es_result verify_exception_info(struct 
>> ghcb *ghcb, struct es_em_ctxt
>>       return ES_VMM_ERROR;
>>   }
>> -static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
>> +static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool 
>> set_ghcb_msr,
>>                         struct es_em_ctxt *ctxt,
>>                         u64 exit_code, u64 exit_info_1,
>>                         u64 exit_info_2)
>> @@ -138,7 +138,14 @@ static enum es_result sev_es_ghcb_hv_call(struct 
>> ghcb *ghcb,
>>       ghcb_set_sw_exit_info_1(ghcb, exit_info_1);
>>       ghcb_set_sw_exit_info_2(ghcb, exit_info_2);
>> -    sev_es_wr_ghcb_msr(__pa(ghcb));
>> +    /*
>> +     * Hyper-V unenlightened guests use a paravisor for communicating 
>> and
>> +     * GHCB pages are being allocated by that paravisor which uses a
>> +     * different MSR and protocol.
> 
> Just to clarify the comment, the paravisor uses the same GHCB MSR and 
> GHCB protocol, it just can't use __pa() to get the address of the GHCB. 
> So I expect that the Hyper-V support sets the address properly before 
> calling this function.
> 
> Thanks,
> Tom
> 
>> +     */
>> +    if (set_ghcb_msr)
>> +        sev_es_wr_ghcb_msr(__pa(ghcb));
>> +
>>       VMGEXIT();
>>       return verify_exception_info(ghcb, ctxt);
>>
>>