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Message-ID: <0c4f3e87-b138-407b-a271-7f86fef255f6@suse.com>
Date: Tue, 10 Sep 2024 14:26:31 +0200
From: Jan Beulich <jbeulich@...e.com>
To: Juergen Gross <jgross@...e.com>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org,
linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v3 5/7] xen: add capability to remap non-RAM pages to
different PFNs
On 10.09.2024 12:39, Juergen Gross wrote:
> When running as a Xen PV dom0 it can happen that the kernel is being
> loaded to a guest physical address conflicting with the host memory
> map.
>
> In order to be able to resolve this conflict, add the capability to
> remap non-RAM areas to different guest PFNs. A function to use this
> remapping information for other purposes than doing the remap will be
> added when needed.
>
> As the number of conflicts should be rather low (currently only
> machines with max. 1 conflict are known), save the remap data in a
> small statically allocated array.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
Reviewed-by: Jan Beulich <jbeulich@...e.com>
with two cosmetic remarks:
> @@ -792,6 +793,70 @@ int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref *unmap_ops,
> return ret;
> }
>
> +/* Remapped non-RAM areas */
> +#define NR_NONRAM_REMAP 4
> +static struct nonram_remap {
> + phys_addr_t maddr;
> + phys_addr_t paddr;
> + size_t size;
> +} xen_nonram_remap[NR_NONRAM_REMAP] __ro_after_init;
> +static unsigned int nr_nonram_remap __ro_after_init;
I take it this is the canonical placement of section attributes in the
kernel? (In Xen I'd ask for the attributes to be moved ahead of the
identifiers being declared.)
> +/*
> + * Do the real remapping of non-RAM regions as specified in the
> + * xen_nonram_remap[] array.
> + * In case of an error just crash the system.
> + */
> +void __init xen_do_remap_nonram(void)
> +{
> + unsigned int i;
> + unsigned int remapped = 0;
> + const struct nonram_remap *remap = xen_nonram_remap;
> + unsigned long pfn, mfn, end_pfn;
> +
> + for (i = 0; i < nr_nonram_remap; i++) {
> + end_pfn = PFN_UP(remap->paddr + remap->size);
> + pfn = PFN_DOWN(remap->paddr);
> + mfn = PFN_DOWN(remap->maddr);
> + while (pfn < end_pfn) {
> + if (!set_phys_to_machine(pfn, mfn)) {
> + pr_err("Failed to set p2m mapping for pfn=%lx mfn=%lx\n",
> + pfn, mfn);
> + BUG();
Wouldn't panic() get you both in one operation? Or do you expect the call
trace / register state to be of immediate relevance for analysis?
Jan
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