From: Tom Lendacky <[email protected]>
Under the GHCB specification, SEV-ES guests can support string I/O. The
current #VC handler contains this support, so remove the need to unroll
kernel string I/O operations. This will reduce the number of #VC
exceptions generated as well as the number VMEXITS for the guest.
Signed-off-by: Tom Lendacky <[email protected]>
---
arch/x86/mm/mem_encrypt.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index c79e5736ab2b..d55ea77e1ca8 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -474,9 +474,10 @@ void __init mem_encrypt_init(void)
swiotlb_update_mem_attributes();
/*
- * With SEV, we need to unroll the rep string I/O instructions.
+ * With SEV, we need to unroll the rep string I/O instructions,
+ * but SEV-ES supports them through the #VC handler.
*/
- if (sev_active())
+ if (sev_active() && !sev_es_active())
static_branch_enable(&sev_enable_key);
print_mem_encrypt_feature_info();
base-commit: a7e0bdf1b07ea6169930ec42b0bdb17e1c1e3bb0
--
2.30.0
On 2/1/21 12:26 PM, Tom Lendacky wrote:
> From: Tom Lendacky <[email protected]>
>
> Under the GHCB specification, SEV-ES guests can support string I/O. The
> current #VC handler contains this support, so remove the need to unroll
> kernel string I/O operations. This will reduce the number of #VC
> exceptions generated as well as the number VMEXITS for the guest.
>
> Signed-off-by: Tom Lendacky <[email protected]>
> ---
> arch/x86/mm/mem_encrypt.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index c79e5736ab2b..d55ea77e1ca8 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -474,9 +474,10 @@ void __init mem_encrypt_init(void)
> swiotlb_update_mem_attributes();
>
> /*
> - * With SEV, we need to unroll the rep string I/O instructions.
> + * With SEV, we need to unroll the rep string I/O instructions,
> + * but SEV-ES supports them through the #VC handler.
> */
> - if (sev_active())
> + if (sev_active() && !sev_es_active())
> static_branch_enable(&sev_enable_key);
This brings up a question. The name implies that this is a general SEV
related key. However, it's currently only used for the string I/O
operations. If further usage of this key is added in the future, then this
would probably need to be split into two keys, the sev_enable_key and an
sev_unroll_io_key.
Is it worth documenting that in the comment? Or should the key be renamed now?
Thanks,
Tom
>
> print_mem_encrypt_feature_info();
>
> base-commit: a7e0bdf1b07ea6169930ec42b0bdb17e1c1e3bb0
>