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Re: [PATCH v6 3/5] x86/mm: make code robust to future PAT changes
- To: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 5 Jan 2023 15:01:17 +0100
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- Cc: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Tim Deegan <tim@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 05 Jan 2023 14:01:37 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 22.12.2022 23:31, Demi Marie Obenour wrote:
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -6352,6 +6352,11 @@ unsigned long get_upper_mfn_bound(void)
> return min(max_mfn, 1UL << (paddr_bits - PAGE_SHIFT)) - 1;
> }
>
> +
> +/*
Nit: Please avoid introducing double blank lines.
> + * A bunch of static assertions to check that the XEN_MSR_PAT is valid
> + * and consistent with the _PAGE_* macros, and that _PAGE_WB is zero.
This comment is too specific for a function of ...
> + */
> static void __init __maybe_unused build_assertions(void)
... this name, in this file.
> @@ -6361,6 +6366,71 @@ static void __init __maybe_unused
> build_assertions(void)
> * using different PATs will not work.
> */
> BUILD_BUG_ON(XEN_MSR_PAT != 0x050100070406ULL);
> +
> + /*
> + * _PAGE_WB must be zero for several reasons, not least because Linux
> + * PV guests assume it.
> + */
> + BUILD_BUG_ON(_PAGE_WB);
> +
> +#define PAT_ENTRY(v)
> \
> + (BUILD_BUG_ON_ZERO(((v) < 0) || ((v) > 7)) +
> \
> + (0xFF & (XEN_MSR_PAT >> (8 * (v)))))
> +
> + /* Validate at compile-time that v is a valid value for a PAT entry */
> +#define CHECK_PAT_ENTRY_VALUE(v)
> \
> + BUILD_BUG_ON((v) < 0 || (v) > 7 ||
> \
See my v5 comments.
Jan
|
