Messages in this thread | | | Subject | Re: [PATCH v5 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active | From | Brijesh Singh <> | Date | Thu, 6 Sep 2018 14:24:32 -0500 |
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On 09/06/2018 01:47 PM, Sean Christopherson wrote: > On Thu, Sep 06, 2018 at 01:37:50PM -0500, Brijesh Singh wrote: >> >> >> On 09/06/2018 09:18 AM, Sean Christopherson wrote: >> .... >> >>>>> >>>>> So are we going to be defining a decrypted section for every piece of >>>>> machinery now? >>>>> >>>>> That's a bit too much in my book. >>>>> >>>>> Why can't you simply free everything in .data..decrypted on !SVE guests? >>>> >>>> That would prevent adding __decrypted to existing declarations, e.g. >>>> hv_clock_boot, which would be ugly in its own right. A more generic >>>> solution would be to add something like __decrypted_exclusive to mark >>>> data that is used if and only if SEV is active, and then free the >>>> SEV-only data when SEV is disabled. >>> >>> Oh, and we'd need to make sure __decrypted_exclusive is freed when >>> !CONFIG_AMD_MEM_ENCRYPT, and preferably !sev_active() since the big >>> array is used only if SEV is active. This patch unconditionally >>> defines hv_clock_dec but only frees it if CONFIG_AMD_MEM_ENCRYPT=y && >>> !mem_encrypt_active(). >>> >> >> Again we have to consider the bare metal scenario while doing this. The >> aux array you proposed will be added in decrypted section only when >> CONFIG_AMD_MEM_ENCRYPT=y. If CONFIG_AMD_MEM_ENCRYPT=n then nothng >> gets put in .data.decrypted section. At the runtime, if memory >> encryption is active then .data.decrypted_hvclock will contains useful >> data. >> >> The __decrypted attribute in "" when CONFIG_AMD_MEM_ENCRYPT=n. > > Right, but won't the data get dumped into the regular .bss in that > case, i.e. needs to be freed? >
Yes, the auxiliary array will dumped into the regular .bss when CONFIG_AMD_MEM_ENCRYPT=n. Typically it will be few k, I am not sure if its worth complicating the code to save those extra memory. Most of the distro's have CONFIG_AMD_MEM_ENCRYPT=y anyways.
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