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SubjectRe: [PATCH v5 12/22] x86/virt/tdx: Convert all memory regions in memblock to TDX memory
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On 6/22/22 04:17, Kai Huang wrote:
...
> Also, explicitly exclude memory regions below first 1MB as TDX memory
> because those regions may not be reported as convertible memory. This
> is OK as the first 1MB is always reserved during kernel boot and won't
> end up to the page allocator.

Are you sure? I wasn't for a few minutes until I found reserve_real_mode()

Could we point to that in this changelog, please?

> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index efa830853e98..4988a91d5283 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1974,6 +1974,7 @@ config INTEL_TDX_HOST
> depends on X86_64
> depends on KVM_INTEL
> select ARCH_HAS_CC_PLATFORM
> + select ARCH_KEEP_MEMBLOCK
> help
> Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
> host and certain physical attacks. This option enables necessary TDX
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 1bc97756bc0d..2b20d4a7a62b 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -15,6 +15,8 @@
> #include <linux/cpumask.h>
> #include <linux/smp.h>
> #include <linux/atomic.h>
> +#include <linux/sizes.h>
> +#include <linux/memblock.h>
> #include <asm/cpufeatures.h>
> #include <asm/cpufeature.h>
> #include <asm/msr-index.h>
> @@ -338,6 +340,91 @@ static int tdx_get_sysinfo(struct tdsysinfo_struct *tdsysinfo,
> return check_cmrs(cmr_array, actual_cmr_num);
> }
>
> +/*
> + * Skip the memory region below 1MB. Return true if the entire
> + * region is skipped. Otherwise, the updated range is returned.
> + */
> +static bool pfn_range_skip_lowmem(unsigned long *p_start_pfn,
> + unsigned long *p_end_pfn)
> +{
> + u64 start, end;
> +
> + start = *p_start_pfn << PAGE_SHIFT;
> + end = *p_end_pfn << PAGE_SHIFT;
> +
> + if (start < SZ_1M)
> + start = SZ_1M;
> +
> + if (start >= end)
> + return true;
> +
> + *p_start_pfn = (start >> PAGE_SHIFT);
> +
> + return false;
> +}
> +
> +/*
> + * Walks over all memblock memory regions that are intended to be
> + * converted to TDX memory. Essentially, it is all memblock memory
> + * regions excluding the low memory below 1MB.
> + *
> + * This is because on some TDX platforms the low memory below 1MB is
> + * not included in CMRs. Excluding the low 1MB can still guarantee
> + * that the pages managed by the page allocator are always TDX memory,
> + * as the low 1MB is reserved during kernel boot and won't end up to
> + * the ZONE_DMA (see reserve_real_mode()).
> + */
> +#define memblock_for_each_tdx_mem_pfn_range(i, p_start, p_end, p_nid) \
> + for_each_mem_pfn_range(i, MAX_NUMNODES, p_start, p_end, p_nid) \
> + if (!pfn_range_skip_lowmem(p_start, p_end))

Let's summarize where we are at this point:

1. All RAM is described in memblocks
2. Some memblocks are reserved and some are free
3. The lower 1MB is marked reserved
4. for_each_mem_pfn_range() walks all reserved and free memblocks, so we
have to exclude the lower 1MB as a special case.

That seems superficially rather ridiculous. Shouldn't we just pick a
memblock iterator that skips the 1MB? Surely there is such a thing.
Or, should we be doing something different with the 1MB in the memblock
structure?

> +/* Check whether first range is the subrange of the second */
> +static bool is_subrange(u64 r1_start, u64 r1_end, u64 r2_start, u64 r2_end)
> +{
> + return r1_start >= r2_start && r1_end <= r2_end;
> +}
> +
> +/* Check whether address range is covered by any CMR or not. */
> +static bool range_covered_by_cmr(struct cmr_info *cmr_array, int cmr_num,
> + u64 start, u64 end)
> +{
> + int i;
> +
> + for (i = 0; i < cmr_num; i++) {
> + struct cmr_info *cmr = &cmr_array[i];
> +
> + if (is_subrange(start, end, cmr->base, cmr->base + cmr->size))
> + return true;
> + }
> +
> + return false;
> +}
> +
> +/*
> + * Check whether all memory regions in memblock are TDX convertible
> + * memory. Return 0 if all memory regions are convertible, or error.
> + */
> +static int check_memblock_tdx_convertible(void)
> +{
> + unsigned long start_pfn, end_pfn;
> + int i;
> +
> + memblock_for_each_tdx_mem_pfn_range(i, &start_pfn, &end_pfn, NULL) {
> + u64 start, end;
> +
> + start = start_pfn << PAGE_SHIFT;
> + end = end_pfn << PAGE_SHIFT;
> + if (!range_covered_by_cmr(tdx_cmr_array, tdx_cmr_num, start,
> + end)) {
> + pr_err("[0x%llx, 0x%llx) is not fully convertible memory\n",
> + start, end);
> + return -EINVAL;
> + }
> + }
> +
> + return 0;
> +}
> +
> /*
> * Detect and initialize the TDX module.
> *
> @@ -371,6 +458,19 @@ static int init_tdx_module(void)
> if (ret)
> goto out;
>
> + /*
> + * To avoid having to modify the page allocator to distinguish
> + * TDX and non-TDX memory allocation, convert all memory regions
> + * in memblock to TDX memory to make sure all pages managed by
> + * the page allocator are TDX memory.
> + *
> + * Sanity check all memory regions are fully covered by CMRs to
> + * make sure they are truly convertible.
> + */
> + ret = check_memblock_tdx_convertible();
> + if (ret)
> + goto out;
> +
> /*
> * Return -EINVAL until all steps of TDX module initialization
> * process are done.

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