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SubjectRe: [PATCH v1 1/4] x86/sev: Remove sev_enable_key usage in outs##bwl()/ins##bwl()
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On 11/15/21 6:45 PM, Kuppuswamy Sathyanarayanan wrote:
> String I/O instructions (INS/OUTS) can be used to move blocks of
> data between I/O ports and memory space. But emulation of these
> instructions is not supported in AMD SEV platform. Since these
> instructions are obsolete, hypervisors rarely emulate them. So to
> support the legacy usage, INS/OUTS are unrolled using IN/OUT
> instructions.
>
> Currently, this is implemented by adding a SEV specific static
> key check in outs##bwl()/ins##bwl() macros. Since TDX VM guests
> also need similar support, the implementation needs to be made
> generic using the cc_platform_has() call.
>
> In preparation for adding cc_platform_has() based support, as a
> first step remove the sev_enable_key usage and replace it with
> direct reference to "sev_status".

Probably makes sense to just go directly to the cc_platform_has() call
rather than introduce the usage of sev_status.

So maybe squash patches 1 and 2 into a single patch.

Thanks,
Tom

>
> Since this patch replaces the static key usage, it might lead to
> some performance gap.
>
> Suggested-by: Tom Lendacky <thomas.lendacky@amd.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> ---
> arch/x86/include/asm/io.h | 15 ++++++++-------
> arch/x86/mm/mem_encrypt.c | 11 +----------
> 2 files changed, 9 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> index 5c6a4af0b911..69093a610630 100644
> --- a/arch/x86/include/asm/io.h
> +++ b/arch/x86/include/asm/io.h
> @@ -257,17 +257,18 @@ static inline void slow_down_io(void)
> #endif
>
> #ifdef CONFIG_AMD_MEM_ENCRYPT
> -#include <linux/jump_label.h>
>
> -extern struct static_key_false sev_enable_key;
> -static inline bool sev_key_active(void)
> +extern u64 sev_status;
> +
> +static inline bool is_sev_enabled(void)
> {
> - return static_branch_unlikely(&sev_enable_key);
> + return ((sev_status & MSR_AMD64_SEV_ENABLED) &&
> + !(sev_status & MSR_AMD64_SEV_ES_ENABLED));
> }
>
> #else /* !CONFIG_AMD_MEM_ENCRYPT */
>
> -static inline bool sev_key_active(void) { return false; }
> +static inline bool is_sev_enabled(void) { return false; }
>
> #endif /* CONFIG_AMD_MEM_ENCRYPT */
>
> @@ -301,7 +302,7 @@ static inline unsigned type in##bwl##_p(int port) \
> \
> static inline void outs##bwl(int port, const void *addr, unsigned long count) \
> { \
> - if (sev_key_active()) { \
> + if (is_sev_enabled()) { \
> unsigned type *value = (unsigned type *)addr; \
> while (count) { \
> out##bwl(*value, port); \
> @@ -317,7 +318,7 @@ static inline void outs##bwl(int port, const void *addr, unsigned long count) \
> \
> static inline void ins##bwl(int port, void *addr, unsigned long count) \
> { \
> - if (sev_key_active()) { \
> + if (is_sev_enabled()) { \
> unsigned type *value = (unsigned type *)addr; \
> while (count) { \
> *value = in##bwl(port); \
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 35487305d8af..49e5dfc23785 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -43,8 +43,7 @@ u64 sme_me_mask __section(".data") = 0;
> u64 sev_status __section(".data") = 0;
> u64 sev_check_data __section(".data") = 0;
> EXPORT_SYMBOL(sme_me_mask);
> -DEFINE_STATIC_KEY_FALSE(sev_enable_key);
> -EXPORT_SYMBOL_GPL(sev_enable_key);
> +EXPORT_SYMBOL_GPL(sev_status);
>
> /* Buffer used for early in-place encryption by BSP, no locking needed */
> static char sme_early_buffer[PAGE_SIZE] __initdata __aligned(PAGE_SIZE);
> @@ -499,14 +498,6 @@ void __init mem_encrypt_init(void)
> /* Call into SWIOTLB to update the SWIOTLB DMA buffers */
> swiotlb_update_mem_attributes();
>
> - /*
> - * With SEV, we need to unroll the rep string I/O instructions,
> - * but SEV-ES supports them through the #VC handler.
> - */
> - if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) &&
> - !cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
> - static_branch_enable(&sev_enable_key);
> -
> print_mem_encrypt_feature_info();
> }
>
>

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