From: Dave Hansen <dave.hansen@intel.com>
To: Jinank Jain <jinankjain@linux.microsoft.com>,
seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, jinankjain@microsoft.com,
thomas.lendacky@amd.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: wei.liu@kernel.org, tiala@microsoft.com
Subject: Re: [PATCH] arch/x86: Set XSS while handling #VC intercept for CPUID
Date: Tue, 3 Oct 2023 09:07:06 -0700 [thread overview]
Message-ID: <e7ae2b89-f2c4-e95f-342b-fcf92a2e0ae3@intel.com> (raw)
In-Reply-To: <20231003092835.18974-1-jinankjain@linux.microsoft.com>
On 10/3/23 02:28, Jinank Jain wrote:
...
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index 2eabccde94fb..92350a24848c 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -880,6 +880,9 @@ static enum es_result vc_handle_cpuid(struct ghcb *ghcb,
> if (snp_cpuid_ret != -EOPNOTSUPP)
> return ES_VMM_ERROR;
>
> + if (regs->ax == 0xD && regs->cx == 0x1)
> + ghcb_set_xss(ghcb, 0);
The spec talks about leaf 0xD, but not the subleaf:
> XSS is only required to besupplied when a request forCPUID 0000_000D
> is made andthe guest supports the XSS MSR(0x0000_0DA0).
Why restrict this to subleaf (regx->cx) 1?
Second, XCR0 is being supplied regardless of the CPUID leaf. Why should
XSS be restricted to 0xD while XCR0 is universally supplied?
Third, why is it OK to supply a garbage (0) value? If the GHCB field is
required it's surely because the host *NEEDS* the value to do something.
Won't a garbage value potentially confuse the host?
next prev parent reply other threads:[~2023-10-03 16:07 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-03 9:28 [PATCH] arch/x86: Set XSS while handling #VC intercept for CPUID Jinank Jain
2023-10-03 9:40 ` Ingo Molnar
2023-10-03 16:07 ` Dave Hansen [this message]
2023-10-03 18:27 ` Tom Lendacky
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