On 21/01/2026 2:28 pm, Alejandro Vallejo wrote:
> Add missing scaffolding to enable BusLock Threshold. That is:
>
> * Add general_intercepts_3.
> * Add missing VMEXIT
> * Adjust NPF perf counter base to immediately after the buslock counter
>
> Signed-off-by: Alejandro Vallejo <[email protected]>
> Reviewed-by: Teddy Astie <[email protected]>
> ---
> v2:
> * s/general intercepts 2/general intercepts 3/
> * removed _thresh suffix
> * added missing _svm_ infix in the SVM feature
> ---
> xen/arch/x86/hvm/svm/vmcb.h | 15 +++++++++++++--
> xen/arch/x86/include/asm/hvm/svm.h | 2 ++
> xen/arch/x86/include/asm/perfc_defn.h | 2 +-
> 3 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/svm/vmcb.h b/xen/arch/x86/hvm/svm/vmcb.h
> index ba554a9644..231f9b1b06 100644
> --- a/xen/arch/x86/hvm/svm/vmcb.h
> +++ b/xen/arch/x86/hvm/svm/vmcb.h
> @@ -65,6 +65,11 @@ enum GenericIntercept2bits
> GENERAL2_INTERCEPT_RDPRU = 1 << 14,
> };
>
> +/* general 3 intercepts */
All these comments are useless. I'll do a prep patch to delete them, so
they can't be used as a source of patch nitpicking.
> +enum GenericIntercept3bits
> +{
> + GENERAL3_INTERCEPT_BUS_LOCK_THRESH = 1 << 5,
> +};
>
> /* control register intercepts */
> enum CRInterceptBits
> @@ -289,6 +294,7 @@ enum VMEXIT_EXITCODE
> VMEXIT_MWAIT_CONDITIONAL= 140, /* 0x8c */
> VMEXIT_XSETBV = 141, /* 0x8d */
> VMEXIT_RDPRU = 142, /* 0x8e */
> + VMEXIT_BUS_LOCK = 165, /* 0xa5 */
> /* Remember to also update VMEXIT_NPF_PERFC! */
> VMEXIT_NPF = 1024, /* 0x400, nested paging fault */
> /* Remember to also update SVM_PERF_EXIT_REASON_SIZE! */
> @@ -405,7 +411,8 @@ struct vmcb_struct {
> u32 _exception_intercepts; /* offset 0x08 - cleanbit 0 */
> u32 _general1_intercepts; /* offset 0x0C - cleanbit 0 */
> u32 _general2_intercepts; /* offset 0x10 - cleanbit 0 */
> - u32 res01[10];
> + u32 _general3_intercepts; /* offset 0x14 - cleanbit 0 */
> + u32 res01[9];
> u16 _pause_filter_thresh; /* offset 0x3C - cleanbit 0 */
> u16 _pause_filter_count; /* offset 0x3E - cleanbit 0 */
> u64 _iopm_base_pa; /* offset 0x40 - cleanbit 1 */
> @@ -489,7 +496,10 @@ struct vmcb_struct {
> u64 nextrip; /* offset 0xC8 */
> u8 guest_ins_len; /* offset 0xD0 */
> u8 guest_ins[15]; /* offset 0xD1 */
> - u64 res10a[100]; /* offset 0xE0 pad to save area */
> + u64 res10a[8]; /* offset 0xE0 */
> + u16 bus_lock_thresh; /* offset 0x120 */
> + u16 res10b[3]; /* offset 0x122 */
> + u64 res10c[91]; /* offset 0x128 pad to save area */
>
This wants a matching hunk:
diff --git a/xen/arch/x86/hvm/svm/vmcb.c b/xen/arch/x86/hvm/svm/vmcb.c
index cbee10d0463d..8734fd2bca11 100644
--- a/xen/arch/x86/hvm/svm/vmcb.c
+++ b/xen/arch/x86/hvm/svm/vmcb.c
@@ -430,9 +430,14 @@ static void __init __maybe_unused build_assertions(void)
/* Build-time check of the VMCB layout. */
BUILD_BUG_ON(sizeof(vmcb) != PAGE_SIZE);
+
+ /* Control area */
BUILD_BUG_ON(offsetof(typeof(vmcb), _pause_filter_thresh) != 0x03c);
BUILD_BUG_ON(offsetof(typeof(vmcb), _vintr) != 0x060);
BUILD_BUG_ON(offsetof(typeof(vmcb), event_inj) != 0x0a8);
+ BUILD_BUG_ON(offsetof(typeof(vmcb), bus_lock_count) != 0x120);
+
+ /* State Save area */
BUILD_BUG_ON(offsetof(typeof(vmcb), es) != 0x400);
BUILD_BUG_ON(offsetof(typeof(vmcb), _cpl) != 0x4cb);
BUILD_BUG_ON(offsetof(typeof(vmcb), _cr4) != 0x548);
Despite all the comments, it's very easy to res[] arrays wrong when
splitting them like this.
I can fold on commit.
~Andrew
