linux-kernel - Re: [PATCH 1/2] x86/mm: Allow guest.enc_status_change

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Message-ID: <8a9ca63b-60d8-050c-30b5-a9bdc7a26940@linux.intel.com>
Date:   Thu, 25 May 2023 16:28:08 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        dave.hansen@...el.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de
Cc:     decui@...rosoft.com, rick.p.edgecombe@...el.com, seanjc@...gle.com,
        thomas.lendacky@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/mm: Allow guest.enc_status_change_prepare() to
 fail

Hi,

On 5/25/23 3:58 PM, Kirill A. Shutemov wrote:
> TDX code is going to provide guest.enc_status_change_prepare() that is
> able to fail.

You can add some info about why you need this?

> 
> Add a way to return an error from the callback.
> 
> While there, fix enc_status_change_finish_noop(). It is defined as
> always-fail now which doesn't make sense for noop.

IMO, since the above change is an independent fix, I think it is better to
split this into a separate patch.

Other than above suggestions, the rest of the changes looks fine.

> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: stable@...r.kernel.org
> ---
>  arch/x86/include/asm/x86_init.h | 2 +-
>  arch/x86/kernel/x86_init.c      | 4 ++--
>  arch/x86/mm/mem_encrypt_amd.c   | 4 +++-
>  arch/x86/mm/pat/set_memory.c    | 3 ++-
>  4 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> index 88085f369ff6..1ca9701917c5 100644
> --- a/arch/x86/include/asm/x86_init.h
> +++ b/arch/x86/include/asm/x86_init.h
> @@ -150,7 +150,7 @@ struct x86_init_acpi {
>   * @enc_cache_flush_required	Returns true if a cache flush is needed before changing page encryption status
>   */
>  struct x86_guest {
> -	void (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
> +	bool (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
>  	bool (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
>  	bool (*enc_tlb_flush_required)(bool enc);
>  	bool (*enc_cache_flush_required)(void);
> diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
> index d82f4fa2f1bf..64664311ac2b 100644
> --- a/arch/x86/kernel/x86_init.c
> +++ b/arch/x86/kernel/x86_init.c
> @@ -130,8 +130,8 @@ struct x86_cpuinit_ops x86_cpuinit = {
>  
>  static void default_nmi_init(void) { };
>  
> -static void enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { }
> -static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return false; }
> +static bool enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { return true; }
> +static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return true; }
>  static bool enc_tlb_flush_required_noop(bool enc) { return false; }
>  static bool enc_cache_flush_required_noop(void) { return false; }
>  static bool is_private_mmio_noop(u64 addr) {return false; }
> diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
> index e0b51c09109f..4f95c449a406 100644
> --- a/arch/x86/mm/mem_encrypt_amd.c
> +++ b/arch/x86/mm/mem_encrypt_amd.c
> @@ -319,7 +319,7 @@ static void enc_dec_hypercall(unsigned long vaddr, int npages, bool enc)
>  #endif
>  }
>  
> -static void amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
> +static bool amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
>  {
>  	/*
>  	 * To maintain the security guarantees of SEV-SNP guests, make sure
> @@ -327,6 +327,8 @@ static void amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool
>  	 */
>  	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP) && !enc)
>  		snp_set_memory_shared(vaddr, npages);
> +
> +	return true;
>  }
>  
>  /* Return true unconditionally: return value doesn't matter for the SEV side */
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 7159cf787613..b8f48ebe753c 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -2151,7 +2151,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
>  		cpa_flush(&cpa, x86_platform.guest.enc_cache_flush_required());
>  
>  	/* Notify hypervisor that we are about to set/clr encryption attribute. */
> -	x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
> +	if (!x86_platform.guest.enc_status_change_prepare(addr, numpages, enc))
> +		return -EIO;
>  
>  	ret = __change_page_attr_set_clr(&cpa, 1);
>  

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer