| Message ID | d854fa4415ca6d2b5d055d0b29b147a5cdf232f7.1705965635.git.isaku.yamahata@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM TDX basic feature support | expand |
On 1/23/2024 7:53 AM, isaku.yamahata@intel.com wrote: > From: Yuan Yao <yuan.yao@intel.com> > > TDX module internally uses locks to protect internal resources. It tries > to acquire the locks. If it fails to obtain the lock, it returns > TDX_OPERAND_BUSY error without spin because its execution time limitation. > > TDX SEAMCALL API reference describes what resources are used. It's known > which TDX SEAMCALL can cause contention with which resources. VMM can > avoid contention inside the TDX module by avoiding contentious TDX SEAMCALL > with, for example, spinlock. Because OS knows better its process > scheduling and its scalability, a lock at OS/VMM layer would work better > than simply retrying TDX SEAMCALLs. > > TDH.MEM.* API except for TDH.MEM.TRACK operates on a secure EPT tree and > the TDX module internally tries to acquire the lock of the secure EPT tree. > They return TDX_OPERAND_BUSY | TDX_OPERAND_ID_SEPT in case of failure to > get the lock. TDX KVM allows sept callbacks to return error so that TDP > MMU layer can retry. > > TDH.VP.ENTER is an exception with zero-step attack mitigation. Normally > TDH.VP.ENTER uses only TD vcpu resources and it doesn't cause contention. > When a zero-step attack is suspected, it obtains a secure EPT tree lock and > tracks the GPAs causing a secure EPT fault. Thus TDG.VP.ENTER may result Should be TDH.VP.ENTER. > in TDX_OPERAND_BUSY | TDX_OPERAND_ID_SEPT. Also TDH.MEM.* SEAMCALLs may > result in TDX_OPERAN_BUSY | TDX_OPERAND_ID_SEPT. s/TDX_OPERAN_BUSY/TDX_OPERAND_BUSY > > Retry TDX TDH.MEM.* API and TDH.VP.ENTER on the error because the error is > a rare event caused by zero-step attack mitigation and spinlock can not be > used for TDH.VP.ENTER due to indefinite time execution. Does it retry TDH.VP.ENTER on SEPT busy? I didn't see the related code in this patch. > > Signed-off-by: Yuan Yao <yuan.yao@intel.com> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com> > --- > arch/x86/kvm/vmx/tdx_ops.h | 48 +++++++++++++++++++++++++++++++------- > 1 file changed, 39 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/kvm/vmx/tdx_ops.h b/arch/x86/kvm/vmx/tdx_ops.h > index cd12e9c2a421..53a6c3f692b0 100644 > --- a/arch/x86/kvm/vmx/tdx_ops.h > +++ b/arch/x86/kvm/vmx/tdx_ops.h > @@ -52,6 +52,36 @@ static inline u64 tdx_seamcall(u64 op, struct tdx_module_args *in, > void pr_tdx_error(u64 op, u64 error_code, const struct tdx_module_args *out); > #endif > > +/* > + * TDX module acquires its internal lock for resources. It doesn't spin to get > + * locks because of its restrictions of allowed execution time. Instead, it > + * returns TDX_OPERAND_BUSY with an operand id. > + * > + * Multiple VCPUs can operate on SEPT. Also with zero-step attack mitigation, > + * TDH.VP.ENTER may rarely acquire SEPT lock and release it when zero-step > + * attack is suspected. It results in TDX_OPERAND_BUSY | TDX_OPERAND_ID_SEPT > + * with TDH.MEM.* operation. Note: TDH.MEM.TRACK is an exception. > + * > + * Because TDP MMU uses read lock for scalability, spin lock around SEAMCALL > + * spoils TDP MMU effort. Retry several times with the assumption that SEPT > + * lock contention is rare. But don't loop forever to avoid lockup. Let TDP > + * MMU retry. > + */ > +#define TDX_ERROR_SEPT_BUSY (TDX_OPERAND_BUSY | TDX_OPERAND_ID_SEPT) > + > +static inline u64 tdx_seamcall_sept(u64 op, struct tdx_module_args *in, > + struct tdx_module_args *out) > +{ > +#define SEAMCALL_RETRY_MAX 16 > + int retry = SEAMCALL_RETRY_MAX; > + u64 ret; > + > + do { > + ret = tdx_seamcall(op, in, out); > + } while (ret == TDX_ERROR_SEPT_BUSY && retry-- > 0); > + return ret; > +} > + > static inline u64 tdh_mng_addcx(hpa_t tdr, hpa_t addr) > { > struct tdx_module_args in = { > @@ -74,7 +104,7 @@ static inline u64 tdh_mem_page_add(hpa_t tdr, gpa_t gpa, hpa_t hpa, hpa_t source > }; > > clflush_cache_range(__va(hpa), PAGE_SIZE); > - return tdx_seamcall(TDH_MEM_PAGE_ADD, &in, out); > + return tdx_seamcall_sept(TDH_MEM_PAGE_ADD, &in, out); > } > > static inline u64 tdh_mem_sept_add(hpa_t tdr, gpa_t gpa, int level, hpa_t page, > @@ -87,7 +117,7 @@ static inline u64 tdh_mem_sept_add(hpa_t tdr, gpa_t gpa, int level, hpa_t page, > }; > > clflush_cache_range(__va(page), PAGE_SIZE); > - return tdx_seamcall(TDH_MEM_SEPT_ADD, &in, out); > + return tdx_seamcall_sept(TDH_MEM_SEPT_ADD, &in, out); > } > > static inline u64 tdh_mem_sept_rd(hpa_t tdr, gpa_t gpa, int level, > @@ -98,7 +128,7 @@ static inline u64 tdh_mem_sept_rd(hpa_t tdr, gpa_t gpa, int level, > .rdx = tdr, > }; > > - return tdx_seamcall(TDH_MEM_SEPT_RD, &in, out); > + return tdx_seamcall_sept(TDH_MEM_SEPT_RD, &in, out); > } > > static inline u64 tdh_mem_sept_remove(hpa_t tdr, gpa_t gpa, int level, > @@ -109,7 +139,7 @@ static inline u64 tdh_mem_sept_remove(hpa_t tdr, gpa_t gpa, int level, > .rdx = tdr, > }; > > - return tdx_seamcall(TDH_MEM_SEPT_REMOVE, &in, out); > + return tdx_seamcall_sept(TDH_MEM_SEPT_REMOVE, &in, out); > } > > static inline u64 tdh_vp_addcx(hpa_t tdvpr, hpa_t addr) > @@ -133,7 +163,7 @@ static inline u64 tdh_mem_page_relocate(hpa_t tdr, gpa_t gpa, hpa_t hpa, > }; > > clflush_cache_range(__va(hpa), PAGE_SIZE); > - return tdx_seamcall(TDH_MEM_PAGE_RELOCATE, &in, out); > + return tdx_seamcall_sept(TDH_MEM_PAGE_RELOCATE, &in, out); > } > > static inline u64 tdh_mem_page_aug(hpa_t tdr, gpa_t gpa, hpa_t hpa, > @@ -146,7 +176,7 @@ static inline u64 tdh_mem_page_aug(hpa_t tdr, gpa_t gpa, hpa_t hpa, > }; > > clflush_cache_range(__va(hpa), PAGE_SIZE); > - return tdx_seamcall(TDH_MEM_PAGE_AUG, &in, out); > + return tdx_seamcall_sept(TDH_MEM_PAGE_AUG, &in, out); > } > > static inline u64 tdh_mem_range_block(hpa_t tdr, gpa_t gpa, int level, > @@ -157,7 +187,7 @@ static inline u64 tdh_mem_range_block(hpa_t tdr, gpa_t gpa, int level, > .rdx = tdr, > }; > > - return tdx_seamcall(TDH_MEM_RANGE_BLOCK, &in, out); > + return tdx_seamcall_sept(TDH_MEM_RANGE_BLOCK, &in, out); > } > > static inline u64 tdh_mng_key_config(hpa_t tdr) > @@ -307,7 +337,7 @@ static inline u64 tdh_mem_page_remove(hpa_t tdr, gpa_t gpa, int level, > .rdx = tdr, > }; > > - return tdx_seamcall(TDH_MEM_PAGE_REMOVE, &in, out); > + return tdx_seamcall_sept(TDH_MEM_PAGE_REMOVE, &in, out); > } > > static inline u64 tdh_sys_lp_shutdown(void) > @@ -335,7 +365,7 @@ static inline u64 tdh_mem_range_unblock(hpa_t tdr, gpa_t gpa, int level, > .rdx = tdr, > }; > > - return tdx_seamcall(TDH_MEM_RANGE_UNBLOCK, &in, out); > + return tdx_seamcall_sept(TDH_MEM_RANGE_UNBLOCK, &in, out); > } > > static inline u64 tdh_phymem_cache_wb(bool resume)
diff --git a/arch/x86/kvm/vmx/tdx_ops.h b/arch/x86/kvm/vmx/tdx_ops.h index cd12e9c2a421..53a6c3f692b0 100644 --- a/arch/x86/kvm/vmx/tdx_ops.h +++ b/arch/x86/kvm/vmx/tdx_ops.h @@ -52,6 +52,36 @@ static inline u64 tdx_seamcall(u64 op, struct tdx_module_args *in, void pr_tdx_error(u64 op, u64 error_code, const struct tdx_module_args *out); #endif +/* + * TDX module acquires its internal lock for resources. It doesn't spin to get + * locks because of its restrictions of allowed execution time. Instead, it + * returns TDX_OPERAND_BUSY with an operand id. + * + * Multiple VCPUs can operate on SEPT. Also with zero-step attack mitigation, + * TDH.VP.ENTER may rarely acquire SEPT lock and release it when zero-step + * attack is suspected. It results in TDX_OPERAND_BUSY | TDX_OPERAND_ID_SEPT + * with TDH.MEM.* operation. Note: TDH.MEM.TRACK is an exception. + * + * Because TDP MMU uses read lock for scalability, spin lock around SEAMCALL + * spoils TDP MMU effort. Retry several times with the assumption that SEPT + * lock contention is rare. But don't loop forever to avoid lockup. Let TDP + * MMU retry. + */ +#define TDX_ERROR_SEPT_BUSY (TDX_OPERAND_BUSY | TDX_OPERAND_ID_SEPT) + +static inline u64 tdx_seamcall_sept(u64 op, struct tdx_module_args *in, + struct tdx_module_args *out) +{ +#define SEAMCALL_RETRY_MAX 16 + int retry = SEAMCALL_RETRY_MAX; + u64 ret; + + do { + ret = tdx_seamcall(op, in, out); + } while (ret == TDX_ERROR_SEPT_BUSY && retry-- > 0); + return ret; +} + static inline u64 tdh_mng_addcx(hpa_t tdr, hpa_t addr) { struct tdx_module_args in = { @@ -74,7 +104,7 @@ static inline u64 tdh_mem_page_add(hpa_t tdr, gpa_t gpa, hpa_t hpa, hpa_t source }; clflush_cache_range(__va(hpa), PAGE_SIZE); - return tdx_seamcall(TDH_MEM_PAGE_ADD, &in, out); + return tdx_seamcall_sept(TDH_MEM_PAGE_ADD, &in, out); } static inline u64 tdh_mem_sept_add(hpa_t tdr, gpa_t gpa, int level, hpa_t page, @@ -87,7 +117,7 @@ static inline u64 tdh_mem_sept_add(hpa_t tdr, gpa_t gpa, int level, hpa_t page, }; clflush_cache_range(__va(page), PAGE_SIZE); - return tdx_seamcall(TDH_MEM_SEPT_ADD, &in, out); + return tdx_seamcall_sept(TDH_MEM_SEPT_ADD, &in, out); } static inline u64 tdh_mem_sept_rd(hpa_t tdr, gpa_t gpa, int level, @@ -98,7 +128,7 @@ static inline u64 tdh_mem_sept_rd(hpa_t tdr, gpa_t gpa, int level, .rdx = tdr, }; - return tdx_seamcall(TDH_MEM_SEPT_RD, &in, out); + return tdx_seamcall_sept(TDH_MEM_SEPT_RD, &in, out); } static inline u64 tdh_mem_sept_remove(hpa_t tdr, gpa_t gpa, int level, @@ -109,7 +139,7 @@ static inline u64 tdh_mem_sept_remove(hpa_t tdr, gpa_t gpa, int level, .rdx = tdr, }; - return tdx_seamcall(TDH_MEM_SEPT_REMOVE, &in, out); + return tdx_seamcall_sept(TDH_MEM_SEPT_REMOVE, &in, out); } static inline u64 tdh_vp_addcx(hpa_t tdvpr, hpa_t addr) @@ -133,7 +163,7 @@ static inline u64 tdh_mem_page_relocate(hpa_t tdr, gpa_t gpa, hpa_t hpa, }; clflush_cache_range(__va(hpa), PAGE_SIZE); - return tdx_seamcall(TDH_MEM_PAGE_RELOCATE, &in, out); + return tdx_seamcall_sept(TDH_MEM_PAGE_RELOCATE, &in, out); } static inline u64 tdh_mem_page_aug(hpa_t tdr, gpa_t gpa, hpa_t hpa, @@ -146,7 +176,7 @@ static inline u64 tdh_mem_page_aug(hpa_t tdr, gpa_t gpa, hpa_t hpa, }; clflush_cache_range(__va(hpa), PAGE_SIZE); - return tdx_seamcall(TDH_MEM_PAGE_AUG, &in, out); + return tdx_seamcall_sept(TDH_MEM_PAGE_AUG, &in, out); } static inline u64 tdh_mem_range_block(hpa_t tdr, gpa_t gpa, int level, @@ -157,7 +187,7 @@ static inline u64 tdh_mem_range_block(hpa_t tdr, gpa_t gpa, int level, .rdx = tdr, }; - return tdx_seamcall(TDH_MEM_RANGE_BLOCK, &in, out); + return tdx_seamcall_sept(TDH_MEM_RANGE_BLOCK, &in, out); } static inline u64 tdh_mng_key_config(hpa_t tdr) @@ -307,7 +337,7 @@ static inline u64 tdh_mem_page_remove(hpa_t tdr, gpa_t gpa, int level, .rdx = tdr, }; - return tdx_seamcall(TDH_MEM_PAGE_REMOVE, &in, out); + return tdx_seamcall_sept(TDH_MEM_PAGE_REMOVE, &in, out); } static inline u64 tdh_sys_lp_shutdown(void) @@ -335,7 +365,7 @@ static inline u64 tdh_mem_range_unblock(hpa_t tdr, gpa_t gpa, int level, .rdx = tdr, }; - return tdx_seamcall(TDH_MEM_RANGE_UNBLOCK, &in, out); + return tdx_seamcall_sept(TDH_MEM_RANGE_UNBLOCK, &in, out); } static inline u64 tdh_phymem_cache_wb(bool resume)