linux-kernel - Re: [PATCH v9 18/19] KVM: selftests: Add ucall support for TDX

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Message-ID: <23effdc0-1fbe-430d-b570-bc927b10fcf2@linux.intel.com>
Date: Wed, 3 Sep 2025 09:07:57 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Sagi Shahar <sagis@...gle.com>, linux-kselftest@...r.kernel.org,
 Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>,
 Ackerley Tng <ackerleytng@...gle.com>, Ryan Afranji <afranji@...gle.com>,
 Andrew Jones <ajones@...tanamicro.com>,
 Isaku Yamahata <isaku.yamahata@...el.com>,
 Erdem Aktas <erdemaktas@...gle.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Roger Wang <runanwang@...gle.com>, Oliver Upton <oliver.upton@...ux.dev>,
 "Pratik R. Sampat" <pratikrajesh.sampat@....com>,
 Reinette Chatre <reinette.chatre@...el.com>, Ira Weiny
 <ira.weiny@...el.com>, Chao Gao <chao.gao@...el.com>,
 Chenyi Qiang <chenyi.qiang@...el.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Subject: Re: [PATCH v9 18/19] KVM: selftests: Add ucall support for TDX

On 9/2/2025 11:45 PM, Sean Christopherson wrote:
> On Wed, Aug 27, 2025, Binbin Wu wrote:
>> On 8/21/2025 12:29 PM, Sagi Shahar wrote:
>>> @@ -46,11 +69,23 @@ void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
>>>    {
>>>    	struct kvm_run *run = vcpu->run;
>>> -	if (run->exit_reason == KVM_EXIT_IO && run->io.port == UCALL_PIO_PORT) {
>>> -		struct kvm_regs regs;
>>> +	switch (vm_type) {
>>> +	case KVM_X86_TDX_VM:
>>> +		if (vcpu->run->exit_reason == KVM_EXIT_MMIO &&
>>> +		    vcpu->run->mmio.phys_addr == host_ucall_mmio_gpa &&
>>> +		    vcpu->run->mmio.len == 8 && vcpu->run->mmio.is_write) {
>>> +			uint64_t data = *(uint64_t *)vcpu->run->mmio.data;
>>> +
>>> +			return (void *)data;
>>> +		}
>>> +		return NULL;
>> My first thought was how did SEV_ES or SNP work for this since they are not
>> able to get RDI neither.
>> Then I had a check in sev_smoke_test.c, both guest_sev_es_code() and
>> guest_snp_code() call GUEST_ASSERT(), which finally calls ucall_assert(), but
>> in test_sev(), the code doesn't handle ucall for SEV_ES or SNP.
>> Does it mean GUEST_ASSERT() is currently not working and ignored for SEV_ES
>> and SNP? Or did I miss anything?
> GUEST_ASSERT() "works" for -ES and -SNP in the sense that it generates as test
> failure due to the #VC not being handled (leads to SHUTDOWN).  But you're correct
> that ucall isn't functional yet.  x86/sev_smoke_test.c fudges around lack of ucall
> by using the GHCB MSR protocol to signal "done".
>
>          /*
>           * TODO: Add GHCB and ucall support for SEV-ES guests.  For now, simply
>           * force "termination" to signal "done" via the GHCB MSR protocol.
>           */
>          wrmsr(MSR_AMD64_SEV_ES_GHCB, GHCB_MSR_TERM_REQ);
>          vmgexit();
>
OK, thanks for the explanation!