linux-kernel - Re: [PATCH v13 12/13] x86/kvmclock: Abort SecureTSC enabled guest when kvmclock is selected

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Message-ID: <8039c16d-eb1f-c416-a6f3-521107e2aae9@amd.com>
Date: Tue, 22 Oct 2024 09:58:03 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Tom Lendacky <thomas.lendacky@....com>, linux-kernel@...r.kernel.org,
 bp@...en8.de, x86@...nel.org, kvm@...r.kernel.org
Cc: mingo@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com,
 pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v13 12/13] x86/kvmclock: Abort SecureTSC enabled guest
 when kvmclock is selected

On 10/21/2024 8:30 PM, Tom Lendacky wrote:
> On 10/21/24 00:51, Nikunj A Dadhania wrote:
>> SecureTSC enabled guests should use TSC as the only clock source, terminate
>> the guest with appropriate code when clock source switches to hypervisor
>> controlled kvmclock.
>>
>> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
>> ---
>>  arch/x86/include/asm/sev-common.h | 1 +
>>  arch/x86/include/asm/sev.h        | 2 ++
>>  arch/x86/coco/sev/shared.c        | 3 +--
>>  arch/x86/kernel/kvmclock.c        | 9 +++++++++
>>  4 files changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
>> index 6ef92432a5ce..ad0743800b0e 100644
>> --- a/arch/x86/include/asm/sev-common.h
>> +++ b/arch/x86/include/asm/sev-common.h
>> @@ -207,6 +207,7 @@ struct snp_psc_desc {
>>  #define GHCB_TERM_SVSM_VMPL0		8	/* SVSM is present but has set VMPL to 0 */
>>  #define GHCB_TERM_SVSM_CAA		9	/* SVSM is present but CAA is not page aligned */
>>  #define GHCB_TERM_SECURE_TSC		10	/* Secure TSC initialization failed */
>> +#define GHCB_TERM_SECURE_TSC_KVMCLOCK	11	/* KVM clock selected instead of Secure TSC */
>>  
>>  #define GHCB_RESP_CODE(v)		((v) & GHCB_MSR_INFO_MASK)
>>  
>> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
>> index 34f7b9fc363b..783dc57f73c3 100644
>> --- a/arch/x86/include/asm/sev.h
>> +++ b/arch/x86/include/asm/sev.h
>> @@ -537,6 +537,7 @@ static inline int handle_guest_request(struct snp_msg_desc *mdesc, u64 exit_code
>>  
>>  void __init snp_secure_tsc_prepare(void);
>>  void __init securetsc_init(void);
>> +void __noreturn sev_es_terminate(unsigned int set, unsigned int reason);
>>  
>>  #else	/* !CONFIG_AMD_MEM_ENCRYPT */
>>  
>> @@ -586,6 +587,7 @@ static inline int handle_guest_request(struct snp_msg_desc *mdesc, u64 exit_code
>>  
>>  static inline void __init snp_secure_tsc_prepare(void) { }
>>  static inline void __init securetsc_init(void) { }
>> +static inline void sev_es_terminate(unsigned int set, unsigned int reason) { }
>>  
>>  #endif	/* CONFIG_AMD_MEM_ENCRYPT */
>>  
>> diff --git a/arch/x86/coco/sev/shared.c b/arch/x86/coco/sev/shared.c
>> index c2a9e2ada659..d202790e1385 100644
>> --- a/arch/x86/coco/sev/shared.c
>> +++ b/arch/x86/coco/sev/shared.c
>> @@ -117,8 +117,7 @@ static bool __init sev_es_check_cpu_features(void)
>>  	return true;
>>  }
>>  
>> -static void __head __noreturn
>> -sev_es_terminate(unsigned int set, unsigned int reason)
>> +void __head __noreturn sev_es_terminate(unsigned int set, unsigned int reason)
>>  {
>>  	u64 val = GHCB_MSR_TERM_REQ;
>>  
>> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
>> index 5b2c15214a6b..b135044f3c7b 100644
>> --- a/arch/x86/kernel/kvmclock.c
>> +++ b/arch/x86/kernel/kvmclock.c
>> @@ -21,6 +21,7 @@
>>  #include <asm/hypervisor.h>
>>  #include <asm/x86_init.h>
>>  #include <asm/kvmclock.h>
>> +#include <asm/sev.h>
>>  
>>  static int kvmclock __initdata = 1;
>>  static int kvmclock_vsyscall __initdata = 1;
>> @@ -150,6 +151,14 @@ bool kvm_check_and_clear_guest_paused(void)
>>  
>>  static int kvm_cs_enable(struct clocksource *cs)
>>  {
>> +	/*
>> +	 * For a guest with SecureTSC enabled, the TSC should be the only clock
>> +	 * source. Abort the guest when kvmclock is selected as the clock
>> +	 * source.
>> +	 */
>> +	if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
> 
> if (WARN_ON(cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC)))
> 
> so that the guest sees something as well?

Sure, will add.

Regards
Nikunj