Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 2 Nov 2022 13:03:42 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Michael Kelley <mikelley@microsoft.com>
Cc:     hpa@zytor.com, kys@microsoft.com, haiyangz@microsoft.com,
        sthemmin@microsoft.com, wei.liu@kernel.org, decui@microsoft.com,
        luto@kernel.org, peterz@infradead.org, davem@davemloft.net,
        edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
        lpieralisi@kernel.org, robh@kernel.org, kw@linux.com,
        bhelgaas@google.com, arnd@arndb.de, hch@infradead.org,
        m.szyprowski@samsung.com, robin.murphy@arm.com,
        thomas.lendacky@amd.com, brijesh.singh@amd.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        Tianyu.Lan@microsoft.com, kirill.shutemov@linux.intel.com,
        sathyanarayanan.kuppuswamy@linux.intel.com, ak@linux.intel.com,
        isaku.yamahata@intel.com, dan.j.williams@intel.com,
        jane.chu@oracle.com, seanjc@google.com, tony.luck@intel.com,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        linux-hyperv@vger.kernel.org, netdev@vger.kernel.org,
        linux-pci@vger.kernel.org, linux-arch@vger.kernel.org,
        iommu@lists.linux.dev
Subject: Re: [PATCH 02/12] x86/ioapic: Gate decrypted mapping on
 cc_platform_has() attribute
Message-ID: <Y2Jqrr54LfKqHu1n@liuwe-devbox-debian-v2>
References: <1666288635-72591-1-git-send-email-mikelley@microsoft.com>
 <1666288635-72591-3-git-send-email-mikelley@microsoft.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1666288635-72591-3-git-send-email-mikelley@microsoft.com>
Precedence: bulk

On Thu, Oct 20, 2022 at 10:57:05AM -0700, Michael Kelley wrote:
> Current code always maps the IOAPIC as shared (decrypted) in a
> confidential VM. But Hyper-V guest VMs on AMD SEV-SNP with vTOM
> enabled use a paravisor running in VMPL0 to emulate the IOAPIC.
> In such a case, the IOAPIC must be accessed as private (encrypted).
> 
> Fix this by gating the IOAPIC decrypted mapping on a new
> cc_platform_has() attribute that a subsequent patch in the series
> will set only for Hyper-V guests. The new attribute is named
> somewhat generically because similar paravisor emulation cases
> may arise in the future.
> 
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>

Reviewed-by: Wei Liu <wei.liu@kernel.org>

> ---
>  arch/x86/kernel/apic/io_apic.c |  3 ++-
>  include/linux/cc_platform.h    | 13 +++++++++++++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index a868b76..d2c1bf7 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -2686,7 +2686,8 @@ static void io_apic_set_fixmap(enum fixed_addresses idx, phys_addr_t phys)
>  	 * Ensure fixmaps for IOAPIC MMIO respect memory encryption pgprot
>  	 * bits, just like normal ioremap():
>  	 */
> -	flags = pgprot_decrypted(flags);
> +	if (!cc_platform_has(CC_ATTR_HAS_PARAVISOR))
> +		flags = pgprot_decrypted(flags);
>  
>  	__set_fixmap(idx, phys, flags);
>  }
> diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
> index cb0d6cd..b6c4a79 100644
> --- a/include/linux/cc_platform.h
> +++ b/include/linux/cc_platform.h
> @@ -90,6 +90,19 @@ enum cc_attr {
>  	 * Examples include TDX Guest.
>  	 */
>  	CC_ATTR_HOTPLUG_DISABLED,
> +
> +	/**
> +	 * @CC_ATTR_HAS_PARAVISOR: Guest VM is running with a paravisor
> +	 *
> +	 * The platform/OS is running as a guest/virtual machine with
> +	 * a paravisor in VMPL0. Having a paravisor affects things
> +	 * like whether the I/O APIC is emulated and operates in the
> +	 * encrypted or decrypted portion of the guest physical address
> +	 * space.
> +	 *
> +	 * Examples include Hyper-V SEV-SNP guests using vTOM.
> +	 */
> +	CC_ATTR_HAS_PARAVISOR,
>  };
>  
>  #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
> -- 
> 1.8.3.1
>